Swimming is not allowed in Lake Chabot, a northern California backup reservoir; apparently, however, it is usually not actively discouraged: several members of a recent fourth of July outing to the lake had been intending to take a dip -- only to find new signs up, saying in no uncertain terms that any contact with the water in the reservoir was, at this time, strictly prohibited, as it was considered to be toxic.

Three healthy dogs had recently ingested small quantities of the green, slimy, gross, smelly stuff, and died.

The park authorities are not advertising this too widely; in fact many visiting dog owners say they are not advertising it enough, and have taken it upon themselves to hand out warnings to other people bringing their pets.

Lake Chabot is not the only freshwater body to become infested this year with the toxin-producing algae -- the same family of algae responsible for the largest algae bloom ever recorded, which has been killing thousands of marine animals and fish recently and is still raging. It stretches all the way from Santa Barbara to Alaska, and bloom may be responsible for all the mortality events along the coast since late 2014.

Read more here: including analysis, backstory, original (hopefully humorous) graphical teaching aid (biology), and complete list of sources.