Habitat/spawning grounds have been lost
Much of the native habitat and spawning ground for Hudson River fish species has been lost due to the dredging of the shipping channel and the filling of coastline and wetlands by the US Army Corps of Engineers and railroads.

Low dissolved oxygen
Oxygen levels in the Hudson River are decreasing because of increases in temperature and other nonnatural causes such as sewage overflows caused by outmoded combined sewer and stormwater systems.

Power plants with once-through cooling
An antiquated system still used to cool many of the Hudson River power plants. These systems draw water from the Hudson, the water absorbs heat, and then is discharged back into the river at an elevated temperature. This technology requires billions of gallons of river water per day, and can kill billions of fish that are impinged on the plant’s intake screens or entrained when drawn through cooling systems.

The river is warming
Increased average temperatures may advance or delay breeding seasons, encourage breeding in the wrong place, inhibit fish migration, and even jeopardize the existence of certain species, such as the Atlantic tomcod and the rainbow smelt.

Overfishing
Occurs when the number of fish taken from a given population exceeds the stock’s ability to replenish itself. Continued overfishing on the river and in the ocean causes a population to decline towards extinction.

Ocean bycatch
Occurs when an ocean fishery, directed to catch a certain species of fish, inadvertently catches another type of fish in its nets. Further study is needed to determine the extent and location of fisheries that catch Hudson River fish species as bycatch.

The invasive zebra mussel
The zebra mussel is blamed for having changed the food web within the Hudson River, resulting in reduced food resources.