Last Updated on 8 December 2022
Dr Dave Dawson, Wimbledon Park’s local ecologist and environmental scientist, writes about the problems of blue-green algae.
Wimbledon Park is a very popular place to walk dogs, but beware! In September 2022, a dog nearly died after drinking water from the brook. There was a bloom of blue-green algae in the lake, which had flowed down to contaminate the brook. The dog required urgent veterinary treatment, but remained seriously disabled from the effects of the algal toxin. Dogs can drink the water and inadvertently take in the toxins. So, dogs are at considerable risk and can die. People, too, are advised to avoid contact with any bloom.
Warning notices were put up by LB Merton, but it is difficult for anyone to determine when there is a risk. This is because the blooms are only obvious when the wind blows a surface scum to the lake edge. There can be danger even when the algae are dispersed in the water and no bloom is obvious. Often the blue-green algae are not toxic, so the risk is difficult to confirm except when an incident occurs. In recent years, three species of blue-green algae have been abundant in the lake between May and September, a long period when precautions may be needed.
Can we prevent the growth of blue-green algae? Yes, it is possible. These blooms depend on high levels of nitrate and phosphate pollution in the lake. This favours the blue-greens over waterweeds and non-toxic algae. The causative nitrate and phosphate enter the lake mainly in water from tributaries. Citizen science investigations over the last five years have shown that phosphate levels in the lake are high, but that nitrate levels are usually so low as to limit algal growth. So, the blue-greens may be responding to increases in nitrate pollution.
Everyone in the catchment of the lake should avoid polluting the surface water drains. There are three main underground tributaries to the lake. Two of these originate on the edge of Wimbledon Common and flow down through suburbia, picking up surface water on the way. The third comes from the All England tennis site west of Church Road. There is no routine testing of the water in any of these, nor of water draining off the golf course into the lake. As there are very many surface water sumps in the suburban catchment, it is difficult to prevent pollutants entering the suburban pipes, but the All England tennis is in one ownership and pollutants from there are readily controlled. The All England do not monitor their pipe, however.
The bad news is that the current planning application for intensive tennis development on the golf course will result in a great increase in nutrients draining into the lake. There will be greater use of chemicals and much more irrigation. The increased drainage from the intensively managed land will be treated, but is insufficient to make much difference to the pollution. Even worse, the proposed method to remove sediment from the bottom of the lake will release pollution that’s currently locked away, contaminating the lake seriously. Approval of the All England’s plans will make the nutrient problem worse. It’s not too late to prevent these plans from harming our lake and putting our dogs at risk, not to mention anglers, water sports users and children playing in the brook and waterfall.
The dog poisoning incident was reported extensively on Nextdoor Wimbledon Park in September. Further details of the lake and its algae can be found in my submissions on the AELTC planning application for intensive lawn tennis development:
The water quality and biodiversity of Wimbledon Park Lake, December 2021.
Proposed development of Wimbledon Park Lake and surrounds, June 2022
The opinions expressed in this post reflect the views of the author.