The concern with Phos-Chek comes from the product sticking to the plants and trees leaves and or roots. When the fire retardant is on the plants it changes the flammability of the plant which slows and or stops the process of combustion for that plant. Of course in long term effects with that fertilizer attached to the plants that survived the fire they now suffer to survive past the fire as well. So we are back to losing plants and trees which create the canopies that protect the fish habitats and protect them from natural heat from sunlight.
How does fire retardant itself affect the fish? Studies have been done that show how fire retardants affect wildlife including fish. These retardant chemicals have been found to be toxic to fish and other aquatic life. The fire retardant can kill fish as well as chemically alter the soil, and feed harmful algae blooms. The chemicals have even been found to help the spread of some invasive plants into the fish's habitat. These Retardant drops are in very large quantities at times in a one week period CalFire reported dropping 2.7 million gallons of Phos-Chek.