This site is useful to find information about dissolved oxygen and the types of tests that are administered to determine the dissolved oxygen level.

This activity introduces students to the complex chemistry of estuarine water. Students investigate how chemical and physical water quality factors-pH, temperature, dissolved oxygen, and salinity-change and interact over varying time...

This site from the U.S. Geological Survey provides great definitions of seven measurements that can be taken on water. Includes pH, dissolved oxygen, and turbidity. Click Home to access the site in Spanish.