The Red Salton Sea
Some red / pink algae here in what appears to have been a harbor in the Salton Sea. Needless to say, I did NOT go boating or swimming in this part of the lake. The circular patterns seen ashore are the remains of tilapia nests. Tilapia are (I believe) the only species of fish that have managed to survive the hypersaline water of the Salton Sea.
Cyanobacteria, sometimes called blue-green algae, have been around for billions of years, and can also be red, purple, brown or pink. They can live in everything from snow to the ring of water around a lawn sprinkler. But as large-scale agriculture and improved testing technology have surged, "toxic algae" are being recognized as a growing problem worldwide. Phosphorous and nitrogen are the main culprits, and can be present in human or animal waste too.