Operational Aspects of Biological Weed Control in Salt River Project Canals

SRP delivers a million acre ft (1200 million cubic meters) of water annually to 250,000 acres (100,000 ha) in central Arizona through approximately 130 miles (210 km) of canals and 1200 miles (1930 km) of laterals. Water usage in the SRP system has shifted from primarily agricultural use to use as a drinking water source. Environmental regulations prohibit the use of most chemical herbicides. SRP has used white amur (Ctenopharyngodon idella) to control extensive aquatic weed growth in most of the canal system for ten years and has found them to be environmentally friendly and cost effective. Environmental regulations require the fish be sterile (triploid) and be physically contained within the canal system to avoid migration into natural rivers and streams. To qualify as a closed system, the canal system has been modified to include electric and physical fish barriers. Methods have been developed to economically and safely move the fish to different reaches of the system for maintenance purposes or to relocate fish that have moved downstream. Weed growth and fish population are monitored and fish are moved to maintain effective weed control throughout the system. The fish grow to as large as 4 feet (>1m) long and 50 lbs (22 kg), and have a life expectancy of 15 years. White amur are stocked at a rate of 35 fish per surface acre and are restocked at approximately 20% per year. Fish losses occur due to injuries caused by relocation activities, angling, and occasional chemical contamination. The use of white amur limits the use of chemical algaecides for taste and odor control. White amur have been shown to adequately control aquatic weed growth. SRP continues to expand reaches stocked with fish and to improve safety and efficiency of fish management.