Restoration & Grass Carp

Devils Lake was faced with reduced water quality and rampant weed growth, so a plan to restore the lake was written in 1986. The restoration plan for Devils Lake includes:
• Biological control of vegetation with Grass Carp

Devils Lake at Horseshoe Bay before Grass Carp.
Devils Lake at Horseshoe Bay after Grass Carp.

• Control of nutrient sources including septic drainfields, fertilizers, detergents and animal wastes
• Watershed management to limit sediment input
• Public education and involvement
• Interagency coordination

Chinese Grass Carp (White Amur) - Biological Control of Vegetation

Grass Carp, also known as Chinese White Amur.
Common Names: Chinese Grass Carp or White Amur
Scientific Name: Ctenopharyngodon idella

APPEARANCE: Dark brown to dark gray on top, lighter to cream color below with slight gold-silver sheen on side. Oblong body with moderate to large scales, rounded belly and broad head. Diamond pattern on side. Jaws have simple thick lips. Dorsal and anal fins are short and without spines.
NATIVE HABITAT: Natural range is eastern China and Soviet Union. They prefer warm water densely vegetated inshore areas 3 - 9 feet in depth and fast flowing, turbid rivers.
AGE AND SIZE: Standard lengths are 23 to 26 inches in females and 20 to 24 inches in males. Grass Carp have been known to grow much larger under ideal conditions. They may live over 20 years but in their native habitat the average age ranges from 5 to 11 years. Those stocked in Devils Lake are a sterile hybrid and are unable to reproduce.
STOCKING: Grass Carp were initially stocked in Devils Lake at a density of approximately 40 fish per acre. The grass carp were 8 to 11 inch triploid grass carp. Grass Carp have been stocked three times in Devils Lake as follows:
  1) 10,000 in September of 1986
  2) 17,090 in March of 1987
  3)   5,000 in July of 1993
      32,090 TOTAL
DIET: Grass Carp are vegetarian and prefer warm water for feeding. When young, Grass Carp can eat their own body weight in weeds every day.

A Devils Lake Water Improvement District (DLWID) newsletter from 1990 states, "Isham, who was hired more for his political skills than his knowledge of lake restoration, puts the official opposition (to grass carp), down to the fact grass carp were at that time associated with the complete eradication of aquatic weeds, which is equally bad environmentally." "With official approval, backed up by a $250,000 grant from the federal Environmental Protection Agency, 10,000 half-pound carp were purchased from an Arkansas supplier. The other half of the money for the program was provided by local property taxes."

The DLWID Manager's Report stated that, "The weed-eating fish were first introduced in September 1986. After three years of intensive study by the Washington Cooperative Fishery Research Unit, University of Washington, it has been established that the $500,000 program has resulted in effective non-damaging aquatic weed control at a cost savings to the district. Grass carp are commonly used for weed eradication in some parts of the world. The Devils Lake Water Improvement District has demonstrated that this technology can also be used for weed control."

After the 1993 grass carp stocking, DLWID has taken a closer look at the affects of grass carp on lake vegetation. The grass carp have voraciously eaten all the lakes bottom vegetation. One wonders what the grass carp are actually eating. DLWID will be having special meetings to develop a management plan for the grass carp. Today there is minimal plant growth in the lake which causes additional problems for fish cover and various environmental concerns. The goal is to use grass carp to keep a healthy balance of plant growth, not eradication.

The grass carp are sterile and there are no plans for additional stocking. This means future control of aquatic plant growth will need to be by another means to prevent the reoccurrence of the 1980's problem.

Report any deceased grass carp sightings to the Devils Lake Water Improvement District (DLWID) at 994-5330.

Grass Carp in Washington State - all or nothing control option
Success with grass carp in Washington has been variable. Sometimes the same stocking rate results in no control, control, or even complete elimination of all underwater plants. Bonar et. al. found that only 18 percent of 98 Washington lakes stocked with grass carp at a median level of 24 fish per vegetated acre had aquatic plants controlled to an intermediate level. In 39 percent of the lakes, all submersed plant species were eradicated. It has become the consensus among researchers and aquatic plant managers around the country that grass carp are an all or nothing control option. They should be stocked only in waterbodies where complete elimination of all submersed plant species can be tolerated. For more information see

Triploid Grass Carp as a Biological Control of Aquatic Vegetation

Information Exchange Bulletin, US Army Corps of Engineers Waters Experiment Station, Vicksburg, MS
An informative article about grass carp:

University of Florida grass carp information:

Invasive Aquatic Plants
Devils Lake has a long history of aquatic plant problems. Macrophytes (large vascular aquatic plants) obtain their nutrients from bottom sediments. Aquatic plants will always be a management issue for Devils Lake due to the fact that the lake is very shallow and has an abundance of rich nutrients in the bottom sediments. Devils Lake has also been plagued over the years with several invasive or non-native plant species. Invasive nonnative weeds are plants that have been introduced to this region through human activities, and due to aggressive growth patterns and lack of natural enemies in this region, spread rapidly into native plant habitats. This can reduce habitat diversity, food, and shelter for many fish and wildlife species, and the ability of the natural environment to perform a wide variety of important ecological functions.

Two of the most aggressive nonnative aquatic plant species that have been present in Devils Lake include: Eurasian watermilfoil (Myriophyllum spicatum) and Brazilian elodea (Egeria densa). Eurasian watermilfoil reproduces vegetatively. Its invasiveness stems from its ability to regrow from tiny fragments. This exotic species has been known to grow up to 20 feet in length! In the years following the introduction of grass carp there was a drastic change in plant community composition in Devils Lake. Brazilian elodea invaded the lake and completely displaced Eurasian watermilfoil. Click here for more information.

Purple loosestrife
Devils Lake and its shoreline have been invaded by an invasive plant called purple loosestrife. Gardeners planted the plant with its purple flowers, not realizing how disastrous it could be to a lake. Uncontrolled, the plant could spread and fill in the lake. The best method of removal is to totally remove the plant by digging up the root. The Devils Lake Water Improvement District (DLWID) schedules volunteer work days to remove the plant. Click here for more information.

Photos from DLWID.

site map


Copyright © 2003-2011 Preservation Association of Devils Lake (PADL).
All rights reserved.

P.O. Box 36
Lincoln City, OR 97367