The study suggests the causes include global warming and the zebra mussel. But it also says five riverfront power plants destroy millions of fish and fish eggs each year by using river water to cool their equipment.
The study was commissioned by the environmental group Riverkeeper. It has been trying for years to force power plants to upgrade their cooling systems to a closed-cycle type that would use much less water.
A spokesman for one of the plants says the water intake does not affect the river's adult fish population.
