Floating Grebe Nests Receive Help From DWR


Western Grebes, seen on a nest, are shown in the Thermalito Afterbay.

Western Grebes, seen on a nest, are shown in the Thermalito Afterbay. Photo taken July 28, 2020. DWR/2020

During the summer months, a unique bird makes its home in the waters around the Oroville-Thermalito Complex, with a little help from the Department of Water Resources (DWR).


The Western and Clark’s grebes are aquatic birds with distinctive red eyes and pointed yellow beaks. During the summer, they arrive from the Pacific Ocean to nesting areas around the Thermalito Afterbay in Oroville. The grebes nest in shallow waters, attaching their floating nests to aquatic vegetation under the surface.


According to the Audubon Society, reservoirs like Thermalito Afterbay support more than 90 percent of the state’s breeding-grebe population. As climate change and recurrent dry conditions make it difficult to know whether natural water bodies will have sufficient water for successful breeding, reservoirs have become increasingly important for the grebes’ reproduction as they reliably support the aquatic vegetation necessary for nesting.


Unfortunately, fluctuations in water levels at the reservoirs can either leave nests stranded or more susceptible to predators. In 2004, the DWR water managers began testing how deep the Thermalito Afterbay reservoir needed to be to fulfill both the grebes’ nesting needs and the state's hydroelectric and downstream water obligations.


For every year since 2004, DWR has established a goal of keeping water levels more consistent during the birds’ nesting season. This summer, DWR initiated that requirement in July, setting the Thermalito Afterbay water level fluctuation between 131- and 136-feet elevation until the end of the breeding and nesting season in September.


“This voluntary agreement made by DWR management to limit the fluctuation of Afterbay water levels has helped protect this species by ensuring the grebe’s nests stay safe during the nesting season,” said Kevin Moncrief, DWR environmental scientist. “It also reflects DWR’s commitment to addressing wildlife needs in our management of the State Water Project.”


DWR’s voluntary restriction is one of many actions taken by DWR’s Oroville Field Division to protect and enhance wildlife and waterfowl who reside, even temporarily, in the Department’s Oroville-Thermalito Complex. The complex includes Oroville Dam, Lake Oroville, Thermalito Diversion Pool, the Thermalito Forebays and Afterbay, the Oroville Wildlife Area, and the Feather River within the Complex’s boundaries.



Visit our Pixel gallery to view more photos of grebes.