Thank you for using eXtension for your pond question. Blue green algae is a form of cyanobacteria and is considered one of the "Harmful Algal Blooms" that are know to be toxic to animals and fish. they are frequently associated with heavy nutrient loading in a body of water. The result is often water that looks very cloudy and bright green to greenish brown colored.
Algae, string algae, duckweed and the like are indications of a normal healthy pond. Conversely pea soup colored cloudy water ponds in August are suspect.
You are correct in presuming that your frogs would vacate such a place.
Here is a website for more information: https://www.epa.gov/nutrientpollution/effects-dead-zones-and-harmful-algal-blooms