The share of the six-county region that is permanently protected as open space increased from 5.1% in 1990 to 7% in 2000. This represented an addition of 43,600 acres to the 1990 base of 123,400 acres. Protected open space also increased on a per capita basis, from 17 acres per 1,000 residents in 1990 to 21.2 in 2000. Ten percent of the land in Cook and DuPage Counties is protected; Kane has the lowest percentage at 2% of land area. By measuring total protected open space and the amount per capita, the region can identify development trends that might lead to permanent loss of natural environments.

Measurements of the Chicago region’s air quality vary dramatically from year to year but have shown improvement over levels of the 1980s. Twenty-three percent of the region’s ozone monitoring stations in operation for at least 15 years recorded annual readings in 1999 that failed to meet current federal standards. The region’s average daily highs in ozone levels have shown an overall increase in the summer months, rising from .0377 parts per million (ppm) in 1993 to .0438 ppm in 1999. The U.S. Environmental Protection Agency considers exposure to an average ozone level of .085 ppm over eight hours to be potentially harmful, especially for people with respiratory difficulties.

As measured by their ability to support aquatic life and human recreation, 61% of the region’s stream miles were rated in good condition in 1993 through 1997, compared with 45% a decade earlier. Water quality improved or stayed the same in all of the individual watersheds; however, the Lake Michigan watershed and Des Plaines watershed remained in much worse xxxcondition than others in the region. Water quality is a valuable measure of the impact of development and conservation practices in that watershed.

While the measure of water quality shows improvement, significant work remains. The Biological Stream Characterization index, which focuses on the health and diversity of fish populations and other aquatic life, and the presence of pollution-intolerant species, shows that nearly two-thirds of the region’s stream miles have ratings of “moderate,” “limited” or “restricted.” A consortium of the Illinois Environmental Protection Agency, the Illinois Department of Natural Resources and the Illinois Natural History Survey prepared the criteria for that index.