These photos show the Washington Department of Fish & Wildlife (WDFW) conducting a carp population assessment and carp removal study. The purpose of this project is to eliminate carp from Green Lake. Carp have a number of harmful effects on water quality and the ecological health of the lake including:
• A reduction in the long-term effectiveness of the alum treatment to control phosphorus by carp burrowing in the lake bottom and allowing phosphorus to escape into the water,
• Increasing water turbidity as a result of stirring up bottom sediments during feeding activity.

Increased turbidity can: 1) decrease sunlight penetration which reduces aquatic plant growth, 2) reduce plankton production, 3) lower dissolved oxygen levels, 4) increase water temperatures, 5) suffocate fish eggs and young, 6) reduce fish food availability and slow the growth of game species, 7) limit habitat for reed-nesting birds, and 8) decrease angling opportunities for more game fishes.

The study will proceed in three steps:
Step 1: Initial Population Assessment
The objective of the initial population assessment is to determine how many carp exist in Green Lake. Carp are temporarily incapacitated with electric shock. Stunned fish are removed from the lake with a dip net and placed in a live tank where they recover within several minutes. The captured fish are measured and marked with a small fin clip and the fish are released alive back into the lake. Multiple catch and mark surveys are planned over the spring and early summer. During each successive survey the ratio of marked (fin clipped) fish to unmarked fish will be recorded. These data are used in a statistical analysis to estimate population size.

Note, other species of fish (e.g., bass and trout) may be stunned by the electroshocking boat, but are generally unharmed.

Step 2: Carp Removal
After the population assessment is completed, the WDFW crew will use the electroshocking boat and various types of nets to catch and remove carp. This process will occur over several months until the catch of carp diminishes. All carp will be removed and disposed of in appropriate manner because the carp are not considered safe to eat. A recent Washington Department of Ecology study found that toxicants in the tissue of Green Lake carp exceeded criteria for the protection of human health.
See details at: http://www.ecy.wa.gov/biblio/0303012.html

Note, other species of fish that are incidentally caught will be released alive.

Step 3: Final Population Assessment
The WDFW will perform a final population assessment during spring 2005 to evaluate the effectiveness of the carp removal operation. This assessment will repeat the mark and recapture procedure described for Step 1.

About the alum treatment
Learn about our monitoring program

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©2006 Friends of Green Lake, Seattle, Washington
Updated October 19, 2007

Webmaster - Ellen Hewitt