The Sun River drainage is a very large area with a variety of fishery resources. Historic accounts indicate that prior to the arrival of European settlers, there were no fish in the entire watershed upstream from the large natural waterfall at Diversion Dam. Apparently, this spectacular waterfall was too large for fish to jump, hence fish were unable to colonize the many miles of pristine rivers and streams in the mountainous area above the falls. Imagine that…. many miles of pristine rivers and streams with no fish! Originally, the only native gamefish in the river downstream from Diversion Falls were westslope cutthroat trout, arctic grayling, mountain whitefish, and burbot (also known as “ling”).
The settlers got busy stocking fish almost right away. Official records of fish stocking date back to the stocking of brook trout and grayling in the river as early as 1928. However, oldtimers in the area have provided reliable reports of trout stocking in the originally fishless area of the Sun River drainage upstream from Diversion Falls as early as 1902. In the years that followed, lots of rainbow trout and some cutthroat and brown trout were stocked in the watershed. Also, it appears other species like suckers and sculpins were moved above the falls.
Very few of the stocked trout were native to this area of Montana. Brook trout came from their native ranges on the East Coast and in the upper Midwest. Brown trout were imported from Europe. Rainbow trout were brought in from the West Coast. All of these new or exotic species competed with the native cutthroat trout and grayling. Some of them, like brown trout, probably preyed on young cutthroats and grayling. Others, like rainbows, interbred (hybridized) with the native cutthroat, destroying the gene pool. In addition, the construction and operation of the extensive irrigation canal and reservoir systems in the drainage removed substantial amounts of water from the river, which resulted in higher water temperatures and less living space (habitat) for the native trout. As a result of all these problems, native grayling and genetically pure native cutthroat are now extinct in the Sun River and its tributaries. If our forefathers had decided to only stock the native cutthroat and grayling above the falls, those Montana natives would probably still be safe in that sanctuary today. Hindsight is always 20:20. The good news is that recovery projects are now underway for both species in the watershed.
