Why is it important to only change 1 variable at a time?

Testing only one Variable at a time lets you analyze the results of your experiment to see how much a single change affected the result. If you're testing two Variables at a time you won't be able to tell which Variable was responsible for the result.

Explanation:

the wetland preservation movement began in the u.s. in earnest with the clean water act (cwa) of 1972. although not specifically written to protect wetlands, the cwa is comprised of a series of regulations designed to prevent pollutants from contaminating u.s. waters.