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
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