Glen Lake Association seeks help catching giant invasive koi
By Sophie Schwartz
Sun contributor
If you ask any fishing enthusiast what they hope to catch in Glen Lake, most will likely tell you they are seeking perch or bass or perhaps even a pike. However, this summer may be prime time to instead aim for bright orange koi fish, as the invasive species presence is confirmed in the lake for the third summer in a row.
Koi, an invasive species known for their bright coloring, are a domesticated form of carp native to eastern Asia. They resemble oversized goldfish, and hold distinct and striking color patterns of orange, black, white and yellow. Their beautiful appearance makes them extremely popular as pets and in ornamental ponds worldwide. It is believed that the koi likely started off as pets, and made their way into the lake through being purposefully released. A single female can lay up to 400,000 eggs per breeding cycle, allowing for the population of koi to easily proliferate.
This prolific spawning causes intense disruptions within the food chain as resources become scarce for native fish. Koi also have a tendency to stir up lake bottoms as they forage (referred to as “rooting”), which can be harmful to native plant species as well as promoting the growth of invasive plant life. Their presence in the lake can promote algae blooms and lead to decreased water clarity, a critically important aspect of Glen Lake.
In an effort to mitigate this potential damage, the Glen Lake Association (GLA) is asking for the help of the public to locate the invasive koi. As the water becomes warmer, the fish become more active and tracking the population is critical. Photographs of the fish are extremely useful in this process, as each koi bears unique patterns and coloration. These distinctive features help give an idea as to how many koi remain in the lake.
If you spot an orange swimmer in Little Glen Lake, Big Glen Lake or Fisher Lake this summer, you can help the GLA by emailing a photo of the fish along with the date and location of the sighting to contact@glenlakeassociation.org.
GLA Executive Director Kate Gille stresses how important the combined effort of the community is. “Protecting water quality is truly a community effort, and we are grateful for residents’ willingness to help us stop invasive species from spreading. These sighting reports and photos are incredibly valuable; each piece of data helps us better understand how many koi are present in the system and allows us to respond quickly and effectively.”
In recent years, several koi have been removed from the lake, including several large, pre-spawn females each carrying thousands of eggs and, in 2024, a record breaking 24.5 pound fish. The GLA is continuing its partnership with a highly experienced bowfishing team this summer in order to continue the removal of the koi.
To learn more about invasive species prevention and management in the Glen Lake watershed, visit the Glen Lake Association website at glenlakeassociation.org/invasive-species.
