Clean water is fundamental to the health of the Great Lakes. To ensure water quality and availability, research conducted on the Great Lakes provides indicators Exit that help to develop sustainable solutions to the Great Lakes water resource problems.

Beach Closings

When bacteria standards are exceeded, local authorities may close swimming at a beach or issue an advisory that the water is unhealthy for swimming.

Dissolved Oxygen Depletion in Lake Erie

Oxygen is essential for all plants and animals to survive, whether they live on the land or in the water. Aquatic organisms rely on oxygen that is dissolved in the water. In most lakes and streams, the amount of oxygen in the water is continually being replenished by oxygen from the air. Sometimes, however, conditions exist in which the dissolved oxygen in the water is used up by organisms faster than it can be replaced from the air. This occurence puts at risk fish and animals that live on the lake bottom.

Lake Erie Phosphorus

Phosphorus is an essential element for all organisms and is found naturally in tributaries and run-off waters. However, too much phosphorus can lead to over-enrichment with algae and aquatic weeds, and depletion of dissolved oxygen as the excess plant and animal matter die off and decay. The biggest contributors of phosphorus into the lakes are man-made sources such as:

• sewage treatment
• agricultural runoff
• industrial processes

Trophic State

The trophic state of lakes describes the surface water quality.