Lakewide Management Plans

Lake Erie 'Dead Zone'

Lake Erie Dissolved Oxygen Special Study, Summer 2002

image of Lake Erie from Nat'l Oceanic & Atmos. Admin.

Introduction

In June, 2002, the U.S. Environmental Protection Agency in cooperation with many universities and other agencies in the United States and Canada, began an intensive special study to determine the cause of the oxygen depletion in Central Lake Erie.

What is the Problem?

The bottom waters in the Central Basin of Lake Erie become anoxic (without oxygen) in the late summer. Aquatic creatures need oxygen in the water to live. 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. If all the oxygen gets used up, the organisms will suffocate. The configuration of the Central Basin of Lake Erie is partly responsible for the problem, but too many nutrients (especially phosphorus) from human activities is also a major factor.

Historical Oxygen Depletion

The amount of oxygen in the bottom waters of Lake Erie becomes smaller over the summer. In June, oxygen concentrations are relatively high, but by late August or mid-September, many locations are nearly without oxygen. The severity of oxygen depletion varies from year-to-year, depending on water temperature and the thickness of the bottom layer.

The rate at which oxygen is used up over the summer lets us know if conditions are getting better. Progressively lower rates over time will eventually lead to oxygen remaining in the water all summer. These rates are calculated with adjustments for annual differences in water temperature and bottom layer thickness. Although the long-term trend is downward, there hasn’t been any improvement since the late 1980s (more on oxygen depletion in Central Lake Erie).