Cooperative Fish and Wildlife Research Units Program: Montana Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Montana Fishery Project

Georgetown Lake diet study

January 2022 - December 2024


Participating Agencies

  • Montana Fish, Wildlife and Parks

Georgetown Lake is a high elevation reservoir located in southwestern Montana, about 13 kilometers south of the town of Philipsburg. It is about 845 hectares at full pool making it the largest lentic waterbody in the upper Clark Fork River drainage. The fishery is managed as a put, grow, and take fishery for rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis) and as a wild, self-sustaining kokanee salmon (kokanee, Oncorhynchus nerka) fishery. Georgetown Lake routinely ranks in the top 10 in Montana for angling pressure and is equally important as a summer and winter ice-fishing destination. Georgetown Lake is a highly productive reservoir and known for producing large numbers of quality-sized rainbow trout, abundant kokanee, and is a premier location for catching trophy brook trout.
The rainbow trout fishery in Georgetown Lake is sustained by annual stocking from Montana Fish, Wildlife and Parks (MFWP) hatcheries. Rainbow trout spawning occurs in Stuart Mill Creek and North Fork Flint Creek, but little recruitment occurs from these areas. Rainbow trout stocking densities and strains have varied temporally. Gerrard-strain rainbow trout stocking ended in 2009 due to the brood source being determined to not be an actual Gerrard strain. Eggs from a Canadian Gerrard-strain rainbow trout were obtained by MFWP and stocking in Georgetown Lake in 2015. Other strains of rainbow trout used for maintaining the rainbow trout fishery are the Arlee and Eagle Lake strains, which are raised in several production hatcheries in Montana.
The rainbow trout fishery in Georgetown Lake has undergone changes in the previous five years since MFWP began stocking the Canadian Gerrard strain into the system. One of the primary changes has been the increase in average size of rainbow trout. The average length of rainbow trout greater than 300 mm has increased from 363 mm (2004-2015) to 402 mm (2017-2020). This length increase suggests that the use of the Gerrard strain may be improving average size in the fishery.