that dark patch is a benthic algal bloom. this is the river rothay that feeds into the lake. it actually prevents invertebrates from being able to breed on the substrate of the river itself and then, because of that, invertebrates have died and, subsequent to that, fish are dying. matt has started an online petition calling for a ban on sewage pollution in windermere. he said the waters here are close to ecological collapse. i have seen a decline in fish, invertebrates, freshwater vegetation. i have seen otter spraint completely absent of white—clawed crayfish. i have seen dead fish floating down the river past me. it is in a very dire state and it will only get worse. algal blooms come and go, but they are appearing more frequently and they can be very harmful to humans and animals. there are two many main sources of sewage entering windermere. one is from the waste treatment site, and that comes in when we have rain. they call it their storm overflow system. and the other is from septic tanks. there are over 1,500 septic tanks that are around windermere itself