Water quality monitoring is essential to assess the overall health of Lake Hopatcong on a year to year basis, identifying long-term trends or changes in water quality, and quantifying and objectively assessing the success and potential impacts of restoration efforts. In-lake monitoring takes place during the growing season from May through September each year at eleven sampling stations on the lake.
The Lake Hopatcong Commission and its predecessor, the Lake Hopatcong Regional Planning Board, conducted regular water quality monitoring of the lake, going back to the 1980s. Since 2001, this monitoring has been performed by Princeton Hydro, LLC. In 2013 and 2017, the Lake Hopatcong Foundation provided funding to continue the monitoring to prevent a gap in the monitoring data.