The three counties that border Mountain Island Lake have regulations designed to prevent run-off that could damage water quality. Mecklenburg County regulations prohibit cutting trees over two inches in diameter within 100 feet of the shoreline. And no new construction is allowed closer than 100 feet. Gaston County regulations require a 50-foot setback.

In addition to limiting run-off, controlling aquatic weeds is important for a healthy lake. To control hydrilla, which has been a problem especially during drought years, Duke Energy places sterile grass carp in the lake. This natural weed-control program is funded cooperatively by Duke Energy, Charlotte/Mecklenburg Utilities, Gastonia and the North Carolina Department of Environment and Natural Resources. Marine Commission regulations prohibit removing carp from the lake.