Identifying cool water habitats for Allagash River brook trout

The AWWF’s Coldwater Fish Habitat Temperature Monitoring project has documented that much of the mainstem Allagash River becomes unsuitable for brook trout during the summer months when water temperatures rise above 73 degrees Farenheit. Historically, it was assumed that cooler tributaries provided the refuge necessary for these trout to persist.

In August of 2025 and 2026, we expanded our search to pinpoint exactly where brook trout escape the river’s high temperatures. We wanted to determine whether the lower reaches of key tributaries provide critical habitat for survival. Locating these summer thermal refuges is a vital first step in creating a framework for focused conservation efforts, especially amidst changing climate conditions and forest management in the watershed.

During this phase of the study, exploratory surveys were conducted on Whittaker Brook, Schedule Brook, and Five Finger Brook—tributaries previously identified as potential summer refuges. Researchers walked the lower reaches upstream from the river, documenting the number, location, and quality of pools based primarily on depth and cover, as well as noting the presence of brook trout.

In total, approximately 5.5 miles of tributary were surveyed, locating 53 discrete pools. Only 11 of these pools were observed holding brook trout. All trout observed were under 10 inches and located close enough to the river to suggest they were “river” fish escaping high temperatures. These findings indicate that while adult usage varies, these lower tributary reaches may offer essential refuge for sub-adult brook trout.

The complete results of this work, along with recommendations for future temperature monitoring and conservation strategies in the AWW, will be included in the upcoming final report for the Coldwater Fish Habitat Temperature Monitoring project.