Many large thermoelectric power plants were built on the shores of the Great Lakes because the lakes provide easy access to the large volumes of water require for plant cooling. Thermoelectric power generation is the largest use of water in the Great Lakes basin (72% of all water use in 2005), with the majority used as cooling water.¹ Proximity to the coast also allows the plants to receive direct shipments of raw materials for their operations, such as coal.

The primary impact of the coastal power plants stressor in this analysis is harm to fish populations through impingement and entrainment. Power plant operations also alter the physical and chemical characteristics of the near-shore environment due to the potential discharge of pollutants including leachate from coal piles, chemicals from equipment maintenance, and thermal effluent from plant cooling.

Impacts of coastal power plants on fish

Most Great Lakes coastal power plants use once-through cooling technology. Plants withdraw water using large underwater pipes, sometimes located up to 1000 meters offshore, circulate the water through their plants, and then discharge heated water back to the lake. Although once-through cooling is considered a non-consumptive use (because nearly all water withdrawn is returned to the source), these systems can be extremely destructive for fish and other aquatic organisms.

• Impingement occurs when fish near the intake structures are trapped on water intake screens – it often leads to fish mortality.
• Entrainment occurs when smaller fish and eggs that pass through the intake screens are harmed by contact with plant infrastructure or by heat shock.

The magnitude of fish kills caused by power plants is difficult to measure, but it can be very large, on the order of 10-100 million fish lost through impingement and billions of larval fish and fish eggs lost through entrainment. Reported losses for individual plants include:

Mapping coastal power plants as a Great Lakes stressor

Our analysis includes 114 coastal power plants located within 2 km of the Great Lakes shoreline on the assumption that these plants draw water directly from the Lakes or from major tributaries just upstream of their confluence with the Lakes. Power plants in our data set use a variety of primary fuel types and have a wide range of generating capacities.^2,3,4