The Thomas Fork Watershed in Bear Lake County, Idaho, and Lincoln County, Wyoming, is a 144,366-acre agricultural watershed near Bear Lake. This geologically old lake, which is one of Idaho's Special Resource waters, has developed unique physical, chemical, and biological characteristics. It has more endemic fish species than any other lake in North America, including five species found nowhere else in the world. Thomas Fork is a major tributary to the Bear River, immediately upstream from its diversion into Bear Lake. Excessive streambank erosion in the watershed and high nutrient levels in runoff from Thomas Fork and the Bear River have accelerated eutrophication throughout the watershed and lake.
Historical data show the increase of phosphorus and nitrogen in the area.
Bank erosion is largely the result of earlier channel modifications undertaken to support agricultural land uses. When the natural meander patterns of Thomas Fork were broken, severe down-cutting and unstable streambanks exceeded the river's capacity to restore equilibrium. Project description lures local landowners Recently, the Bear Lake Regional Commission began to interest local landowners in streambank restoration. Several farmers and ranchers came forward to begin the project, which was funded through Idaho's section 319 program. Materials removed from the banks were used by area farmers to level the low spots in their fields.