The Sacramento pikeminnow, a native California fish, is the most reviled in the Eel River due to its predation on juvenile salmon and steelhead. Annual volunteer dives track its population, which fluctuates with weather conditions.
- The pikeminnow was illegally introduced to Lake Pillsbury in 1979 and spread throughout the Eel basin by 1986. - The fish thrives in warm water, and the Eel River's altered habitat after the 1964 flood has favored its growth.
- Efforts to control the population include spearing, a weir, and potential dam removal to cut off breeding grounds. Despite being a native species, the pikeminnow is treated as an invasive pest in the Eel River, complicating conservation efforts.