Decade-long eradication effort saves reservoir that provides water supplies, recreation
SACRAMENTO, September 13, 2010 — When it is full, Eastman Lake has 27 miles of shoreline and 151,000 acre-feet of water – plenty for providing local water supplies as well as a range of recreational activities such as fishing, camping, boating and swimming. The surrounding area invites bike and horseback riders, bird watchers, and even a good round of Frisbee golf. Located north of Fresno and southwest of Yosemite, the lake is one of California’s true outdoor gems – but it could have been lost years ago due to infestation by an aquatic weed called hydrilla.
Fortunately, a decade-plus eradication effort by several cooperating agencies has restored the reservoir and its tributary system. Ten years of physically removing the weeds and treating the lakebed and river system to remove this aquatic pest were followed by several more years of intensive monitoring to ensure the hardy weed has not returned. The infestation has now been declared eradicated.
“We would like to thank the local residents, community leaders and other agencies that helped make this lengthy but worthwhile project a success,” said California Department of Food and Agriculture (CDFA) Secretary A.G. Kawamura. “Our staff brought its expertise to bear on this problem, but it took a lot more than just us to get it done. We appreciate all the support we received from residents who gave us access to private property, and we also want to recognize the efforts of the Army Corps of Engineers, the California Department of Fish and Game, the California Department of Boating and Waterways, the county agricultural commissioners, and everyone else who pitched in to make this work.”
Hydrilla is a submerged water weed that grows aggressively, driving out native aquatic plants. It often arrives in a new site on board a fishing or pleasure boat. It can spread easily by breaking apart and drifting to new areas of a lake or river system. Fragments as small as one inch can produce entire new plants. The “tuber,” the part of the plant that rests in the sediment, can survive up to seven years before sprouting—creating a major challenge to eradication efforts.
Once a hydrilla colony begins, it can quickly form deep, tangled mats of plant material that have a variety of economic and ecological impacts. They can reduce the flow of water in rivers, creeks, canals and ditches; clog and damage dams, power plants and other water control structures; interfere with boating and fishing; decrease fish stocks; and even alter the oxygen and acidity levels in the water, threatening fish and triggering algae blooms and die-offs.
Through a biological quirk, hydrilla also indirectly threatens bald eagles, which are known to nest near the northeastern bays of Eastman Lake. Hydrilla encourages the growth of certain toxic blue-green algae, which is eaten by coots (a bird that lives in wetlands and on open water bodies), and the coots are in turn eaten by the eagles, poisoning them.
When hydrilla was first discovered in Eastman Lake in June 1989, it infested approximately 100 acres in scattered patches, mostly along the eastern shoreline. Upstream, approximately 26 miles of the main stem and west fork of the river were infested with hydrilla. Some of the heaviest infestations were at the upper end, a notoriously rugged area.
At that point, the lake’s ecosystem was not in great shape. The region was several years into a drought, so lake levels were low and the fish populations and other wildlife were already feeling the impacts.
The Corps of Engineers worked with CDFA to deliver the water from the lake and bring it to “minimum pool” in late summer 1989. The result was the exposure of approximately 10 acres of heavily infested lake bottom. CDFA treated this area with a soil fumigant, which provided essentially 100% control in the immediate area.
Work in the lakebed continued with hand removal and dredging of plants, along with spot treatments with herbicides, leading to the disappearance of hydrilla from the lake by 1993. The plants would not disappear from the river, however, until 2002.
“The staff knew the entire ecosystem was in a delicate state to begin with, and those upper reaches of the river that feeds the lake would be very hard to get to,” said Kawamura. “But the only way to save that reservoir was to eradicate the hydrilla from the entire system, not just the lakebed. If you miss just one spot, the entire cycle of infestation can repeat itself. As aquatic weeds go, hydrilla is not just a nuisance—it’s a resilient and highly damaging pest.”
Photos of Eastman Lake during and after the hydrilla infestation are available upon request.
California Department of Food and Agriculture Office of Public Affairs
1220 N St., Ste. 214, Sacramento, CA 95814