Benthic macro-invertebrates are bottom-dwelling bugs that can give us a longer and more general view of creek health than water chemistry. Each family of bugs has a different tolerance level to pollution, and by surveying the creek we can better understand the creek’s health over a longer period of time. For example, mayflies have a very low tolerance for pollutants, so if the creek supports a thriving mayfly population, water quality must have been good for some time.