Northeast Region
Maine Fish and Wildlife Conservation Office
2 2
The Clam Shell Liming Project


Maine rivers have been greatly affected by human activity, most notably intensive forestry practices, industrialization and acid rain. Rivers most affected are those in the Downeast region, which are characterized by thin soils and low alkalinity bedrock. With a significantly decreased ability to buffer increasing acidity and nutrient loss, pH levels in these rivers are often low enough to be detrimental to fish health, particularly for environmentally sensitive species such as Brook Trout and Atlantic Salmon.

Inspired by large-scale liming projects in Europe that have shown positive results for streams with similar water quality issues, the Maine Department of Environmental Protection's Salmon Program developed the Clam Shell Liming Project for implementation by Project Salmon Habitat and River Enhancement (SHARE), an NGO well known for restoration activities in Downeast Maine. Maine Fishery Resources Office staff have been providing technical and financial support. Scientists hope that, by treating streams with clam shells as a lasting, calcium carbonate source, they can improve water quality by reducing acidity while also providing better calcium nutrition for fish and neutralizing aluminum and other toxic metals within the system (Whiting 2013).

clamshell site table

Summary of study sites, watershed sizes, and original pH.
Also shown is a summary of clam shell applications, including the calculated "required" dose
and the actual total, "existing and new" applications (shaded columns).

canaan brook graph

Summary of electrofishing results from Canaan Brook,
presented as total number of Brook Trout per habitat
unit. Shells were added for the first time at this site in
2012, the baseline year.

The Project

The project began in 2010 with one site and 2 metric tons of clam shells. Now, five years later in 2014, the study has expanded to nine separate sites treated with more than 10 tons of shells within the Machias and East Machias watersheds of Downeast Maine.

The ultimate goal? To increase biodiversity and improve ecosystem integrity throughout Maine's salmon rivers by using clam shells as a calcium carbonate source.

At each site, approximately 40% of the stream bottom is treated with clam shells, which act as a calcium carbonate source and increases alkalinity within the stream. The clam shells were chosen for their large surface areas and potential to form good habitat for both fish and aquatic invertebrates. Currently, the clam shells appear to be positively impacting a wide range of physical and biological factors within the stream.

Throughout the project, staff and volunteers have been actively monitoring the impacts of clam shell placement on fish abundance, macroinvertebrate diversity, leaf pack decomposition rates and a wide variety of water quality metrics. Please see the following reports and presentations for more information on this project.

invertebrate chart

Summary of macroinvertebrates in leafpacks for
July 2 showing the mean abundances for
the most common groups.

For more details on the project, see the following reports and presentations:

Craig S, McKerley J. Clam Shell Report 2008 to 2009. United States Fish and Wildlife Service. 10 March 2009.

Whiting M. Fourth Annual Report on Project SHARE's Acid Mitigation and Fisheries Restoration Project. Maine Department of Environmental Protection. 21 Jan. 2014.

Whiting M. Preliminary Observations on the Effects of Using Clam Shells for Acid Rain Mitigation in Maine Salmon Streams. Maine Department of Environmental Protection. 15 Jan. 2014.



Last updated: February 29, 2016