Hundreds of birds died in Harrow Lodge Park in the London borough of Havering in July 2013 from a severe bout of botulism.
The extreme hot weather and lack of rainfall had a drastic impact on the levels of oxygen in the water, which meant that the bacteria Clostridium botulinum, which live in river sediment, produced highly poisous toxins.Now experts are dredging the lake, pushing contaminated silt from the bottom of the lake to the northern bank with the aim of cleansing the water in which wildfowl live.
Making the lake deeper increases the amount of water in circulation, making it cooler, cleaner, and allowing the wildfowl to survive hot weather.
The work is expected to be complete by the end of March in time for nesting season.
The council allocated £300,000 for the job last April, but waited until the water was at its coldest point to start work. This is because the toxins are less active and the silt can be moved with the minimum amount of harm to the wildfowl in the lake.
Cabinet member for culture and community engagement councillor Melvin Wallace, who took to the lake for a photo opportunity, said: "This has been an important piece of work that we have wanted to do for a while now, and we’ve waited until the right time. We want to give the wildfowl a better habitat, and this will certainly go a long way towards that."
The process is expected to move around 6,000 cubic meters of silt, the equivalent of six million litres of water.
Once complete, the north bank of the lake will be fenced off, reshaped and landscaped.
The silt pusher used for the work is the only one of its kind in the country, and was selected for the task following consultation with the Environment Agency because of the way it gently pushes the silt to cause the least amount of damage for the lake and its wildlife.
Botulism, which comes in three types, is rare among humans but can be fatal. In England and Wales since 2000, there have been 147 cases of wound botulism (eight deaths), but only seven cases of food-borne botulism (one death) and 11 cases of infant botulism (no deaths). Wound botulism is mostly seen in intravenous drug users and not usually linked to the environment.The other two types are caused by contact with the bacteria in soil or food.