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IMPERIAL IRRIGATION DISTRICT FACT SHEET: Aquatic Weed Control The Imperial Irrigation District's (UD) Environmental Resources Section produces a special,variety of fish 'to control the aquatic weed, hydrilla, that once threatened the continued water supply for Imperial Valley agriculture. Hydrilla Problem Hydrilla was first found in the All- American Canal in 1977 and has become the most serious water weed problem ever faced by the no. The dense, tangled mats of hydrilla can totally'clog and restrict irrigation and drainage channels. Hydrilla is the number one aquatic weed problem in the world today because of its ability to grow up to 10 inches a day during the peak growing season and the lack of effective techniques to control it. To develop methods of combating hydrilla, the UD joined the California Depart- ment of Food and Agriculture and the United States Department of Agriculture in a coopera- tive research/operational program. Ini tial Research During three years of research, beginning in 1981, the District's research team studied the mechanical, chemical and biologi- cal methods of controlling some 350 miles of the weed found in the District's waterways. While the mechanical methods were found to be temporary and expensive and chemical means were found incompatible with agricultural and fishery use, the biological research paid handsome rewards. Triploid Grass Carp Research conducted in cooperation with the Coachella Valley Water District has demonstrated the economy and effectiveness of using triploid (sterile) grass carp to con- sume aquatic vegetation. The UD utilizes the sterile variety to avoid any adverse impacts to the balance of the environment. The fish is called "triploid" because a pressure treatment applied to the fertilized egg results in a third set of chromo- somes, instead of the normal two (diploid) in fertile fish. Fish Stocked Initially, in the summer of 1985,7,800 fish were stocked into about 1.5 miles of the All-American Canal. The high stocking rate resulted in total removal of all hydrilla in that area in about eight weeks. As of January 1994 a total of approximately 110,000 fish have been stocked into liD's water delivery system. Ha tchery Constructed liD's grass carp hatchery was com- pleted in May 1988. About 10,000 to 20,000 stockable grass carp per year are produced at the local facility. Public Information Office . P.O. Box 937 . 333 E. Barioni Blvd. . Imperial, CA 92251 @IlD uses recycled paper. PIO 1994