NEW HAVEN, Conn. — A new environmental report says water quality is improving in parts of Long Island Sound in New York and Connecticut but the sound remains under stress from high nitrogen levels.

The report Thursday from New Haven-based Save the Sound says water quality is poor in the heavily populated New York metropolitan area, but very good in eastern Long Island Sound, where there is better tidal flushing.

Save the Sound executive director Curt Johnson says the report shows progress but also underscores a need to reduce pollution by modernizing septic systems, reducing fertilizer use, and planting shrub buffers along the edge of streams and wetlands to keep pollutants from entering the sound.

Save the Sound’s report gives a letter grade for ecosystem health to each of five sub-regions in the sound.