Projected Warming of Wisconsin Streams Could Negatively Affect Trout

Annual average stream temperatures in the Trout Lake watershed, Wisconsin, could increase from one to three degrees Celsius by the year 2100, which might negatively affect cold water fish like brook trout.  

The U.S. Geological Survey recently modeled the effects of climate change on stream temperatures for three recreational fishing creeks near Eagle River, Wisconsin, from years 2000-2100: Stevenson Creek, North Creek and Upper Allequash Creek. Findings suggest that daily mean stream temperatures in Stevenson Creek, the warmest of the three streams, could become too high to sustain a healthy trout population by the turn of the century. 

“A persistent increase in daily mean stream temperature can affect the diversity of fish species in northern Wisconsin,” said USGS scientist William Selbig. “This study can be used by managers to help make important conservation decisions in the Trout Lake watershed.” 

The new USGS report, authored by Selbig, is published in the journal Science of the Total Environment. 

Summer stream temperature is the most important single factor influencing distribution and production of some cold water fishes. Streams that may currently be suitable as a cold water sport fishery, like those in the new study, could become increasingly fragmented as fish seek refuge from warming water temperatures to less impacted areas. 

Brook trout populations are most stable when temperatures do not exceed 19 degrees Celsius, or about 66 degrees Fahrenheit. Selbig found that the frequency at which daily mean stream temperatures exceeded ideal ranges for brook trout increased for Stevenson Creek and North Creek during the last five years of the study period, especially in the warm summer months of July and August. 

“Some emission scenarios indicate that Stevenson Creek could become too warm to maintain its status as a Class II trout stream,” Selbig said.  

However, the coolest of the three streams, Upper Allequash Creek, appeared resilient to climate warming, with temperatures remaining suitable for cold water fish the majority of time. 

The projections showed that by 2100, annual average temperatures could increase by:

• 1.7 to 3.2 degrees Celsius in Stevenson Creek,
• 1.4 to 2.9 degrees Celsius in North Creek and
• 1.1 to 2.2 degrees Celsius in Upper Allequash Creek. 

For more information on water resources in Wisconsin, please visit the USGS Wisconsin Water Science Center website.