Open water

As other types of habitat have declined, various human activities have increased the amount of open water in the watershed. For instance, the construction of dams and artificial reservoirs has dramatically increased the amount of open water habitat. Quarry activity has also led to a small increase in open water habitat.

Seven artificial reservoirs owned and operated by the GRCA perform some but not all of the functions that were once provided by naturally occurring wetlands and forests. Flood storage and base flow augmention are two key functions provided by artificial reservoirs. The reservoirs hold back flood waters in the spring, saving millions of dollars in damages. They also supply water and keep our rivers flowing during the drier summer and fall periods.

The reservoirs have also led to increased recreational opportunities, including swimming, fishing, birding, and boating. People are now able to lie on a sandy beach and enjoy the vista of open water from nearby trails. The reservoirs and adjacent lands provide conditions suitable for a variety of plants and animals, and contribute to the biological diversity within the watershed.

Reservoirs and other open water features (e.g. stormwater ponds, irrigation ponds) can be both good and bad for biodiversity.

Water levels within reservoirs fluctuate widely, creating staging habitat for waterfowl when they are full of water and temporary habitat for shorebirds during the winter drawdown period. However, water stored in the reservoir can also be warmer. Warmer water holds less oxygen than cool or cold water, and this have an adverse impact on aquatic life.

Wetland restoration, enhancement, and creation can also help increase the amount of open water on the landscape.

Open water facts

• Historic size: 5 square kilometres
• Current size: 29 square kilometres
• Strategy: Manage reservoir properties to replace features and functions provided by naturally occurring forests and wetlands.
• Indicator species: aquatic macrophytes, fishes, amphibians, turtles, waterfowl, herons, shorebirds, osprey, bald eagle