Maine Fishery Resources Office
Northeast Region
Water Temperature Monitoring


Maine rivers have been greatly impacted by human activity, such as timber harvesting, agriculture, and industry. Physical alterations (channelizing, removal of riparian vegetation, etc.) and obstructions (dams, roads) have significantly changed the thermal regime of river systems throughout the state. Ponding above dams, lack of overstory, decreased access to cold water refugia - all of these examples of human impact have impacted river temperatures, greatly affecting habitat suitability for a wide variety of aquatic organisms.

bkt probability graph

Probability of Brook Trout presence based on
maximum summer water temperatures (°C)

Many species have known thresholds; above or below certain temperatures may result in decreased growth, metabolism, and reproductive ability. Knowing the thermal regime of rivers influences the ability to manage for various aquatic species, particularly those that are endangered or threatened. Certain fishes, such as Brook Trout and Atlantic Salmon, are highly sensitive to temperature, particularly when temperatures are sustained above a maximum threshold. For example, temperature limits for Atlantic salmon feeding (positive growth) are between 7.0° ±0.3°C and 22.5° ±0.3°C. (Elliot 1991). Brook Trout exhibit a similar temperature tolerance range, where temperatures below 7°C and above 24°C result in little to no growth (Picard 2003).


old stream temperature map

Water temperature profile of Old Stream, August 27, 2013.


The Project

In 2006, we began monitoring water temperatures within Maine watersheds in order to better understand areas of high and low habitat suitability for target species. To date, we've set out temperature data loggers at 261 sites within the East Machias, Machias and Narraguagus rivers of Downeast Maine. The first stages were based on opportunity: placing the loggers at our aquatic connectivity project sites. In 2011, we began more systematically collecting temperature data in the mainstem and tributaries of high priority rivers, based on their populations of endangered Atlantic Salmon.

With this data, we hope to further prioritize our habitat restoration efforts and increase habitat quality for all aquatic organisms within these systems.


All temperature logger sites (2006 -2014).


emac temperature map

Mainstem water temperatures in the
East Machias. Symbology denotes cumulative
days where the temperatures were >22.5°C.

For more information, see the following reports and presentations.

Craig S. Summary of East Machias Water Temperatures 2013. United States Fish and Wildlife Service. 31 Jan. 2014.

Craig S, Lowery I. Assessing the Efficacy of Fish Presence and Species Composition at GIS-Derived Stream-Road Crossings in Two Low Gradient Headwater Streams in Downeast Maine. US Fish and Wildlife Service, Project SHARE. 27 April 2010.

Craig S. Comparison of Water Temperature within Groundwater versus Non-Groundwater Influenced Salmon Habitat in the Machias River Watershed. 20 March 2013.

Craig S, McKerley J. 43 Washout Water Temperatures. United States Fish and Wildlife Service. 10 Feb. 2014.

Elliott JM. Tolerance and Resistance to Thermal Stress in Juvenile Atlantic Salmon, Salmo salar. Frewshwater Biology 25: 61-70. 1991.

Picard C, Bozek M, and W. Momot. Effectiveness of Using Summer Thermal Indices to Classify and Protect Brook Trout Streams in Northern Ontario. North American Journal of Fisheries Management 23:206-215. 2003.

Stanley J, Trial J. Habitat Suitability Index Models: Nonmigratory Freshwater Life Stages of Atlantic Salmon. Biological Science Report 3. May 1995.

Vaccaro JJ, Maloy KJ. A Thermal Profile Method to Identify Potential Ground-Water Discharge Areas and Preferred Salmonid Habitats for Long River Reaches. USGS, Oregon State University. 2006.

Last updated: March 6, 2014