Up here on the Leek arm of the Caldon canal British Waterways have erected signs warning of Blue/Green Algae. The algae naturally occurs in still freshwater like canals and in hot weather can rapidly spread.
The morning after the signs went up along the towpath i awoke to find the canal covered in a carpet of green.
Contact with affected water can cause allergic reactions, itchy eyes and skin irritation and the advice is to avoid contact if possible and wash hands well if you should get your hands wet from mooring ropes for instance. Also keep dogs out of the water.
The algae will disappear as the weather cools. More info can be found on BW website.
www.britishwaterways.co.uk/newsroom