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Golden Algae Project

Golden alga, (Prymnesium parvum), was first discovered in Arizona in 2005 and has since been identified in a number of urban lakes in the greater Phoenix area and three of the four reservoirs along the Salt River on the Tonto National Forest.  Golden algae are suspected to be the cause of several fish kills that have occurred in these lakes and reservoirs. Under certain environmental stresses, golden algae produce a toxin that negatively affects gill-breathing species such as fish, mollusks, arthropods, and the gill-breathing stage of amphibians. When this occurs fish behave as if there is not enough oxygen in the water. They travel at the top of the water surface or rest on the bottom in edges and shallow areas.  Although golden algae can be toxic for fish they are not a threat to humans.

Golden algae related fish kills in these reservoirs have had huge impacts on fishing conditions and can affect numerous fish species.  Since large fish kills in 2005, there has been a noted decrease in fishing among the three Salt River reservoirs; Saguaro, Canyon, and Apache.  While fishing for yellow bass and catfish is still good, fishermen have noted a decrease in the number and size of largemouth bass caught.

The Salt River is located within the Tonto National Forest.  The Salt River contains four storage reservoirs that form a continuous chain of lakes almost 60 miles long. Roosevelt Lake the upper most reservoir and also the largest in the chain has not yet been affected by Golden Algae.

Apache Lake
Downstream from Roosevelt Lake is the next largest reservoir in the chain.  Apache Lake is entrained by Horse Mesa Dam and is located 65 miles northeast of Phoenix.  Apache Lake was formed in 1927 and is 245,138 acre-feet. Apache Lake is the longest of the three reservoirs at 17 miles total length and has 41 miles of shoreline. 

Canyon Lake
Downstream from Apache Lake sits Canyon Lake.  Canyon Lake is formed by Mormon Flat Dam located 51 miles northeast of Phoenix. Canyon Lake was formed in 1926 and is the smallest of the Salt River Reservoirs measuring 57,852 acre-feet. The lake spans 10 miles with 28 miles of shoreline. 

Saguaro Lake
Fourty-one miles northeast of Phoenix, lies Saguaro Lake.  The lowest reservoir on the Salt River, Saguaro also gets the most recreational use due to it’s proximity to Phoenix. The 69,765 acre-foot lake was created by Stewart Mountain dam in 1930.  Saguaro Lake is 10 miles long and has the smallest amount of shoreline with 22 miles. 

This 3-year study began in May 2007 and has two main objectives: 1) To determine effectiveness of largemouth and smallmouth bass stocking efforts in Saguaro, Canyon, and Apache Lakes, 2) Monitor Fish Kill and associated water quality. 

Fish stocking will occur in the fall and spring for the first two years of this study.  In the fall approximately 20,000 six to eight inch largemouth bass and 3,700 six to eight inch smallmouth bass will be distributed into the three reservoirs.  In the spring more than 200,000 two inch largemouth bass will also be stocked into the reservoirs.  The larger bass will be marked with a coded wire tag, which is a small piece of wire (0.25mm in diameter) that is inserted into the tissue of the fish and can later be detected with a special metal detector called a coded wire tag wand.  The smaller bass, stocked in the spring, will be marked with a protein marker called Oxytetracylene (OTC).  The OTC marks can be identified by looking at the boney structures of the fish under a UV light back in the lab.

AZGFD crew conducting an electrofishing surveys.

To determine the success of our stocking efforts, angler surveys are being performed at all three target lakes; Saguaro, Canyon, and Apache.  The sampling is carried out at random selected times during the weekdays and weekends at three different time periods.  Fishermen are asked a list of questions about their catch and experience.  Any largemouth or smallmouth bass that are harvested are checked for a tag to determine if the fish is naturally reproduced or stocked.  All fish harvested are weighed and measured if permitted, to gain better knowledge on the average size harvested.  The data will be used to determine if stocked fish survive and are caught by anglers, and to estimate catch and harvest on the three reservoirs.

Additional evaluation of our stocking efforts are done through electrofishing and gill net sampling.  These surveys are completed twice a year; once in the fall and once in the spring.  Fish are measured, weighed and all largemouth bass are scanned for a coded wire tag to determine whether or not the fish was stocked.

In an effort to determine cause of golden algae related fish kills, Arizona Game and Fish is working with Arizona Department of Environmental Quality (ADEQ) and other partners to monitor water quality characteristics and algal community composition in Saguaro, Canyon, Apache, and Roosevelt lakes.  Part of this effort will be to enhance existing response system to monitor the timing, location, intensity and duration of fish die-offs and to respond when appropriate.

This study will determine if stocking efforts in Saguaro, Canyon, and Apache Lakes are effective in improving the fishing quality in these reservoirs.  Angler catch rates will be monitored throughout to help determine the best method for future stocking efforts to establish and maintain a thriving fishing environment.  Efforts to determine water quality associated with golden algae toxin release will be helpful to predict future fish kills and to manage stocking efforts.  In addition, a monitoring program will also be established to address calls of fish kills and determine proper protocol for reported kills.

Project Update:
As of January 2009 we have stocked 36,543 six to eight inch largemouth bass and 255,000 two inch largemouth bass between the three reservoirs, as well as 12,521 smallmouth bass ranging from three to ten inches. To date we have interviewed 2,100 anglers. 

Starting January 1, 2009, a protective slot on largemouth and smallmouth bass has been implemented at all three reservoirs.  The protective slot ranges between thirteen and sixteen inches with a limit of harvesting one largemouth/smallmouth bass within the slot.

For more information contact:
Bill Stewart, Arizona Game and Fish Department
5000 W. Carefree Highway, Phoenix, AZ 85086-5000.
Phone: (623) 236-7368       E-mail:

Lorraine Avenetti, Arizona Game and Fish Department
5000 W. Carefree Highway, Phoenix, AZ 85086-5000.
Phone: (623) 236-7514       E-mail:

Kyle Tulisiak, Arizona Game and Fish Department
5000 W. Carefree Highway, Phoenix, AZ 85086-5000.
Phone: (623) 236-7675      E-mail:

Amberle Vasey, Arizona Game and Fish Department
5000 W. Carefree Highway, Phoenix, AZ 85086-5000.
Phone: (623) 236-7664      E-mail:

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