Yes Aileen they also normally put signs up round our way but only if the water is monitored by a warden the problem for me is the areas that have no park warden such as ponds in fields and this is where you have to watch and be aware yourself.
In the past its been confind to the larger lakes and such in this area but I just will not let Jess go near the water when there is a risk of Blue Algea being present but like Sophie he prefers to sit near the water with his sunglasses on reading a good book than to risk getting his paws wet
A Dog died here last year due to Blue Algea the dog got thirsty and before they could stop him he was drinking the water.
Best to be on the safe side and check before hand until the weather cools down a bit.