Green Forests = Blue Water
By Dave Anderson

Heading up to the lake this weekend? July is a prime beach month. New Hampshire has over 900 lakes and ponds over 10 acres in size.

Our forests keep those lakes clean. Research indicates that bacteria and aquatic plants thrive best in shallow, nutrient-rich, warm water lakes. Deep, cold lakes where heavily-forested watersheds filter nutrients from storm water runoff host fewer aquatic plants, contain more dissolved oxygen and have higher water clarity.

From May to September, the NH Department of Environmental Services Beach Inspection Program samples and tests water from 170 freshwater beaches each month. The goal is to protect public health and identify waterborne health risks at public swimming beaches. After rain storms, swimming advisories are issued when water quality standards for bacteria or toxins from blue-green “cyanobacteria” are exceeded.

Watersheds with a high percentage of land area in manicured lawns, roofs, concrete, asphalt roads and parking lots transport nutrients and pollutants like motor oil and pet waste in storm water runoff into streams and lakes faster. A higher percentage of forested open space in a watershed buffers lakes from excessive runoff and nutrient-loading after rainstorms.

Next time you head for a swim in a cold, clean New Hampshire lake, consider the role of the forest growing on the slopes above your favorite swimming hole. Trees do more than provide shade. Forests keep lake water clean!