September 2026

There was just a little rain in the last few days of August, but appreciable rain waited until 22mm fell over four days, 8th to 11th of September. This was still too little to charge up the ground water, but sufficient for grass to resume growth and the lake to rise to within 24mm of the crest of the outfall weir, allowing wave action to cause a little overtopping. So, the watersports finally had regained the 140mm lost to evaporation and seepage over the long, hot drought.

The bird count was done on the 10th, before the effects of the rain on the grass had been seen and there were some remarkably low counts. There were no Canada Geese, Mallards or Black-headed Gulls on the lake, just two gulls and 2 geese on the athletics grass. The trend for the Canada Goose continued their low counts in July and August, but the second lowest September gull count over the last 40 years could well have been an immediate response to the return of significant rain making food available in other London sites. Only one year in the last 40 had no Mallards. There were just 22 Woodpigeons detected, fewer than seen in recent Septembers. In contrast, other species were as numerous as normal for September, with 20 Cormorants and 50 Greylags. The 10 House Sparrows were the highest September count since before the great decline in the London area in the 1990s and the 150 Starlings the highest since September 1989. The sparrow feeds its nestlings on insects and the Starling probes in grassland for invertebrates, so neither would have been expected to do well in a drought year. Some of this could be a taste of years to come. As seen often in the past there were extra Mute Swans being chased off by the resident pair, in this case there were just two interlopers. 

On the 10th, I found a new species in the Dave Lofthouse Glade, bringing the number found there over the last 10 years to 148. This was a seedling Cockspurthorn, a relative of Firefox and Hawthorn. It was mown in the meadow management later in the month. Cockspurthorns are commonly planted and sometimes spread by seed.

Early in the month, a strange notice appeared posted on the security fence between the public park and AELTCs part of Ashen Grove Wood. This tiny bit of ancient woodland is no more hazardous than is Horse Close Wood, which is wholly accessible to the public.

AELTC's precaution may not solely reflect a safety concern?

I did my monthly lake water monitoring on the 14th. This confirmed that the cyanobacterium that dominated from early August, Microcystis aeruginosa, was still abundant across all three of my sampling points, if not blooming, and water clarity remained low. So, the ulrasonic device installed by Merton was not having a noticeable effect. The other main plankton was two species of water flea.

Following drastic management of the hedgerows around the park two years ago, using a flail, a few of us have been managing the hedgerows with hand tools, to see if it's practicable to prevent their incursion over paths or into adjacent grasslands in a way that's better for wildlife and amenity. Quite a lot of work was needed in the Spring and Summer as the hedges sent out long branches in the growing season, but we had much success in keeping the hedges in trim whilst avoiding disturbance to breeding birds and retaining much of the flowering and fruiting as valuable wildlife habitat. Sadly, some of this year's work was undone at a stroke on the 25th.

I came across an Idverde operative trimming the Admiral's hedge, right back to the ugly security fence, taking off all the flowering and fruiting that we had sparred to be enjoyed by passers-by and to provide that valued food for birds and insects. The ground was littered with short stems of Hawthorn, Bramble and other woody species. The fruits of Hawthorn, Rose Hips, Holly and Honeysuckle were being cleared away with the rest of the litter. The ivy on the ground still had Ivy Bees visiting the newly-opened flowers. His job was over and he was clearing up, so it was too late to request a stay. I asked him who commissioned the work and he told me it was Tom of Ideverde. A failure of communication here, following discussions after the flailing incident, everyone had gone on the do other things and we hadn't continued discussing alternatives for hedgerow management. My work was exploratory. I had told others who were volunteering in the park, and interested passers-by, but hadn't reported or made recommendations. The operative didn't need telling that the fruits were being sacrificed, he remarked on that without prompting. He was just following instructions and said he would report my concern back to Tom, now too late for this winter.

My work wasn't wasted, as I had already established that management with hand tools worked and the details of what and where. I'll write up my experiences and see if we can return to discuss hedgerow management. I do believe we can meet everyone's desires on this one. 

 

 

August 2026

The drought and heat hardly went away in August. There was a heatwave on the 13th and 14th and higher than average mean temperatures afterwards, even if nothing above 25C. After no rain since June 27th, just 2mm of rain fell around the 19th August and 7.7mm between the 27th and the end of the month, barely enough to moisten the ground surface and then evaporate away within a day or so. Lake levels were affected. They dropped below the outfall weir crest at the beginning of May and, despite 100mm of rain in June, remained below. The minimum in this drought year occurred at the end of August, just before the return of rain in early September. This was 135mm below the dam crest.

Aphanizominon 

can be seen with the naked eye

 

I sampled the lake water more often than usual, as the heat waves and drought might have resulted in interesting changes. On the 10th there was a big change, as the cyanobacterium that had been blooming since the end of May (Aphanizomenon) had greatly declined. Before concluding that the ultrasonic device installed to control cyanobacteria had been effective, I took a closer look at the data. First, one of my sampling points  was within a few metres of the ultrasonic kit and the two others distant. Yet, the decline was evident at all three. Second, I had observed large numbers of a predator of filamentous cyanobacteria in my sample of 29th July. This doubtless had risen to such large numbers on a diet of Aphanizomenon, so was an alternative explanation for the decline the latter. 

Third, and crucially, I found a bloom of a non-filamentous cyanobacterium on the 10th. This was Mrcrocistis, notorious from often being toxic and much more difficult to detect with the naked eye. It bloomed right to the end of the month. So, the ultrasonic device had been tested first against a species that probably succumbed to a predator and then with another that survived for weeks without any apparent decline. I'd like to see better information before believing ultrasound to be effective in our context. What a pity, the ultrasound kit is based upon a nice bit of science and it would be delightful to think it effective.

It was good to see the distinctive hip of the Burnet Rose in Admiral's hedge just north of the athletics gate. 

 

 

 

My bird count was on the 6th. As in July, numbers of Canada Geese were lower than normal, suggesting a possible adverse effect of heat waves. The waterweed-feeder, the Coot was also in reduced numbers. Unusually, there were no Tufted Ducks to be seen, perhaps an effect of the cyanobacteria, although this species is not a waterweed specialist like the Coot. Perhaps most of these birds went off to greener pastures. Again, as in July, the other two species of goose were as abundant as in previous years. The geese continued to feed on the Great Field in the early morning, only to retreat to the lake as dog walkers arrived, so the geese were finding some food there, perhaps a spindly crop of Perennial Ryegrass seeds.  No other species seemed affected, there being 1 Common Tern, 16 Mallards, 8 Moorhens, 2 Mute Swans, 7 Great Crested Grebes and three Grey Herons. So, there was no strong indication that any bird species was affected by whatever caused the mass death of large Carp. The number and variety of fish-feeding birds showed that fish populations were doing well, despite the death of large Carp and Eels.

Burnet Rose

Someone is campaigning on bird feeding at the lake and notices have been posted with a familiar story. Over a year ago the Friends of Wimbledon Park were approached by an organisation that provides machines to vend "healthy" bird food for people who come to feed the birds. Perhaps they are planning to approach LB Merton for permission to install their machines.

Stories abound on the internet that bread is not suitable nutritionally, pollutes the water and causes the deformity "angel wing". I have often sought expert views on this subject and found nothing but rejection of the, all too popular view on bird nutrition. Nor is there anything going for the story about angel wing. 

Bird feeding, nevertheless, is popular.There is a great social benefit to people feeding birds, attracting them in for viewing, so giving youngsters contact with nature and allowing the disadvantaged and those holding social or religious traditions for feeding to follow their tradition. Many people believe that the birds need our help, and I saw someone in the recent droughts who came with several loafs of bread, claiming that the parched Great Field provided no food. In fact, the geese were out on the Great Field eating the seeds of Perennial Ryegrass in the early mornings right through the drought. As in other, non-drought, years the geese resorted to the lake to feed once dog walkers arrived at around 6am, and it was clear that more food was being provided than the birds could eat. 

At least the pollution caused by uneaten food seemed correct, but this applies equally to the alternatives to bread. The seeds sink out of reach of most birds faster than does bread, so are even more likely to remain uneaten and decay. As the lake and its surrounds provide wild food for the birds, the birds don't need our help. This is especially so in summer when wild foods are growing, but most feeding occurs on fine, weekend days in the summer, just when the birds don't lack food.

Over COVID, when people were asked to maintain social distancing, notices were erected at each end of the promenade to identify a "bird feeding area" and yellow cross-hatching painted on the path around the watersports buildings. The intention was to prevent mixing of watersports activity and those visiting for other reasons. These notices remain, even if the attempted distancing is no longer required, but they acknowledge that bird feeding goes on.

The ideal would be not to feed the waterbirds, or to restrict feeding to small amounts, but persuasion is unlikely to be effective and enforcement would be both discriminatory and disproportionate. We have not seen an effective solution to this conundrum.

 

 

 

 

 

July 2026

The big event of the month was an unprecedented fish mortality. This got extensive publicity locally. Here, I reproduce the summary of my report on the incident. I await further clarification from LB Merton, when they respond to my freedom of information request.

Meanwhile, here I reproduce the summary of my report on the incident. "Fish mortality, Wimbledon Park Lake", completed on 17th August.

The nature and cause of a mass mortality of fish on 8^th July 2026 is described. Some 150 mature Carp, a few European Eels and a few other bottom-feeding fish were killed. 

There have been other mass mortality incidents there in the last 25 years, in which various fish species were involved and all of these have occurred close to the discharge points of the lake tributaries. In contrast, this event was lake-wide, and so was not caused by a short-lived discharge from a tributary. None of the previous mass-mortalities corresponded to high temperatures, but the water temperature this time peaked at 30^oC, or above. A shortage of oxygen (hypoxia) was suggested by the behaviour of the fish and by similar incidents elsewhere in the country, and confirmed by testing the water. Previous monitoring showed plenty of oxygen in the lake water, so hypoxia is rare here. 

The owner of the lake, LB Merton proposed to prevent recurrence by controlling Blue-green algae (cyanobacteria), which were abundant at the time.  But these were equally abundant earlier in the summer and in previous summers, as were heat waves. In contrast to previous heat waves, this mass mortality corresponded to record low wind speeds, so I conclude that three factors came together to kill the fish: abundant cyanobacteria, high temperatures and lack of wind. I checked for other possible correlates with the die-off and found none. 

This work was impeded by the absence of published information on the lake, something that LB Merton could remedy readily. 

The ultimate cause of cyanobacterial abundance was eutrophication of the lake by phosphate, but the main source of this remains unknown. Candidates were: waterfowl defecation, die off of plankton, excess feeding of birds and fish, arrival down the tributaries, atmospheric deposition, and disturbance of sediment on the bottom of the lake. A special study is needed to identify the principal factors. 

The best way to avoid a recurrence of mass mortality would be to reduce phosphate pollution, starting with the easy ways to do this and moving on to the less tractable sources. Meanwhile, LB Merton have trialled aerators and ultrasonic devices, methods without a convincing track record in lakes as large and shallow as ours. Given that oxygen comes back naturally, and cyanobacterial blooms die off naturally, there is a real risk that the devices will be confirmed as the cause of a recovery that was, in fact, a natural occurrence. It is vital that LB Merton should publish the minutes of meetings, studies and advice they have had, so that these, and future, events can be better understood.

I did my monthly bird count on the 16th. I was on the lookout for numbers or behaviour that were affected by the continuing drought, or the mass fish kill. The 100 Canada Geese were well above the long-term average for July, if not a record number. This was an about-turn after the low numbers in the last two years. One wonders whether the birds immigrated to the park because people feed them and their natural grassland food is desiccated in the drought. The 80 Greylags were somewhat more than expected, although not such an excess as the Canadas. Interestingly, 30 of the Greylags were out in the Great Field and making their way back to the lake before gate opening time and dog disturbance. So, they were finding some food in the grassland. As usual, there were many, now well-grown, young Greylags and a remarkably late brood of 2 recently-hatched goslings. In contrast, the 25 Egyptian Geese were around the expected number, despite their similar ecology. The resident pair of Mute Swans was still there. 10 Coots was a remarkably low count for July. Coots feed on the grassland of the golf course, which would have been poor forage in the drought, but also on waterweeds. This could indicate that waterweed growth was poor, forcing the Coots to leave for better foraging elsewhere. There were plenty of fish-feeding species: Cormorants, Grey Herons and Great-crested Grebes, an indication that the mass mortality hit the big Carp harder than it did smaller fish.

It was nice to see Wild Carrot in flower in the Revelstoke Road car park verge and a Nursery Web Spider in the Lofthouse Glade. A nice sighting there was a Hornet Mimic Hoverfly, a Medeterranean migrant species that lives in the nests of wasps and hornets. There were many reports of the Jersey Tiger Moth on social media, and there was one on a tree in Horse Close Wood. Bramble and Elder fruits were ripening. Unlike last year, the small patch of Dog's Mercury in Horse Close Wood was withering in the drought. The Lime trees in Horse Close Wood had already shed their seeds. Squirrels and Wood Pigeons will be short of food. No water was flowing down from the lake outfall, but the surface water tributary from Home Park Road suburbia had a trickle. The park gates were opened at 07:00.

On the 29th, I saw a minor pollution incident just like one I saw in 2023. Wimbledon Park Brook flows through the public park and is fed mainly from the outflow from the lake. The brook was modified as part of the works to make the dam safe in 2022, and a new open channel was constructed to take the outflow. However, there has always been a second flow into that brook, not from the lake, but surface water drainage from the nearby Home Park Road. This enters the brook where it passes by the toilet block. 

Both in 2023 and in this July, this surface water flow was milky, suggesting pollution by paint or concrete. On both occasions I reported the pollution on the Thames Water hotline. In 2023 I was telephoned two hours later with a request that I turn up to the site to show the pollution to their investigation team. By then the pipe was running clear and the milkiness had been dispersed downstream with the more voluminous lake overflow. I pointed out where it had issued and asked them to look at my photograph, which they refused, saying that their job was to evaluate what they themselves saw. So, the pollution was not recognised. 

On the 29th of this month, Thames Water now had an online "chat" for reporting the incident. I took a sample of the water and reported full details of the incident to the chat at 13:20. This was ignored and a bot took me through a protocol of questions that merely duplicated my original report. I asked for a reference number, so I might follow up. This request was ignored. At 14:15 their bot got back to me for a photograph of the incident (a surprise to me given their response in 2023), but I sent one. At 15:15 the bot promised a member of the team within 15 minutes. At 15:54 a new bot claimed to be from the operations team and repeated some of the questions over the following hour. Nothing happened then until 19:33 when a new bot took over and asked about recent rain. It was now 6 hours since my original full report, my frustrated reply was: "No rain for many days as you already know! How about actually investigating the incident. You already have enough information" Their bot replied: "Thanks for your message! I'll connect you to one of the team as soon as they're free. They’re available Monday to Friday, 8am until 5pm". I heard no more. My deduction is that no human saw any of my information and that their bot was designed to give the impression of action whilst kicking the can down the road. This experience was a strong disincentive to reporting pollution. Someone in residential Home Park Road has put pollution into the surface water drains and got away with it. I still have that sample of water!

June 2026

The long Spring drought broke on the evening of the first day of meteorological summer and we had 2.5cm of rain over 24 hours. 

The annual hosting of the tennis queue on the Great Field of the park had even more problems this year than last, despite AELTC having agreed more extensive measures to control the crowd. 

There were three significant issues that I picked up by chance, as I went into the hedgerow that runs south from the brook on the tube line boundary and below the trees around the corner from there bordering the gardens off Home Park Road, in the course of fieldwork. Neither area was fenced.

The first issue was a long queue for the public toilets by the cafe, mostly people from the tennis queue who told me that waiting times were 45 minutes for the AELTC facilities. This competition for the public facility deprived the public using the play areas the ready use of toilets.

 

The second issue might relate to the first issue, or the third. This was extensive, fresh defecation in the two wooded areas: at least 20 places with recent use. This was obviously tennis queue-related, either direct use or displaced public from the play areas.

 

The third issue was new camping equipment hidden and stored neatly in the wooded areas: tents groundsheets, etc. A count of the number of sleeping bags gave an estimate of 15 campers. I presume that the tents were erected at night after security patrols ceased, and on the grass nearby, and tidied away before security visits the following morning. I suspect these were free campers, disliking regulation, but they just might be homeless rough sleepers. I heaped up the kit beside the play area fence and it was cleared away promptly the same morning. 

 

Sadly, it seems that the queue has turned into a poorly controlled festival. I'd like to see the queuers welcomed by being given access to shade, and information on the values of the park, but I suspect social media will spread a story of fun in the sun and cause recurring problems from huge crowds. Reluctantly, I think AELTC should be denied use of the park and the tennis queue relocated to their land. Even then we can expect recurrent problems in the park during the fortnight from overspill. The festival vibe may not fade.