California Department of Fish and Wildlife

Nimbus Fish Hatchery

About the Facility

Fish Weir and Ladder Entrance

Visitors viewing Nimbus Hatchery weir

The fish rack or weir stops the upstream migration of fish because of the limited spawning area between this spot and Nimbus Dam. The rack also guides fish to the ladder entrance.

It is installed in the American River about the middle of September and remains until the run is over. Because the eggs will die before they hatch if the water temperature is too high, the ladder is not opened until the water temperature has cooled to below 60 degrees, usually by the first week of November.


Top of Fish Ladder and Holding Pond Entrance

Fish jumping up fish ladder

Salmon and steelhead jump over twenty steps to the top of the fish ladder. From here, they swim into the holding pond through a v-shaped weir that allows passage into the pond but not out. In some years, more than 10,000 salmon will climb the ladder and enter the holding pond.


Sorting and Spawning Area

Eggs being removed from dead fish

Fish are sorted and spawned on a table in the spawning building at the south end of the holding pond. In the case of salmon, fish ready for spawning are killed. Eggs are more easily and quickly taken when the body cavity is opened by an incision. (All Pacific salmon die after spawning, so killing the fish is not wasteful.)

Sperm or "milt" is squeezed from the male salmon and mixed with the freshly taken eggs to fertilize them. A typical salmon has about 5,000 eggs. Female salmon that are not sexually mature and males not needed for fertilizing eggs are returned to the pond to be sorted the next spawning day.


Hatchery Building

Hatchery staff pouring water into egg incubator

The hatchery building houses fish rearing troughs and egg incubators. Eggs are received from the spawning building, and placed into egg hatching jars. Eggs hatch after 50 to 60 days. For about four weeks the fry subsist by absorbing yolk sacs attached to them. They are then placed in the rearing troughs and fed various dry meals in pellet form.


Raceway Ponds

Children feeding fish in long concrete pond

In these twelve ponds, salmon and steelhead are raised for release into the Sacramento River system. Chinook (king) salmon usually are planted at about six months of age when they are four to six inches long. Each year, nearly four million salmon of this size are trucked and planted in the Sacramento River-San Joaquin Estuary.

Steelhead remain in the ponds about a year until they are eight to twelve inches in length. All steelhead yearlings are normally planted in the Sacramento River in January and February near Rio Vista.