indicator

Water Clarity

Year	Western Narrows (m)	Western Narrows Grade	Eastern Narrows (m)	Eastern Narrows Grade	Western Basin (m)	Western Basin Grade	Central Basin (m)	Central Basin Grade	Eastern Basin (m)	Eastern Basin Grade
2008	1.57	F	2.35	A	2.56	A+	2.86	A+	3.24	A+
Year 2008 Western Narrows (m) 1.57 Western Narrows Grade F Eastern Narrows (m) 2.35 Eastern Narrows Grade A Western Basin (m) 2.56 Western Basin Grade A+ Central Basin (m) 2.86 Central Basin Grade A+ Eastern Basin (m) 3.24 Eastern Basin Grade A+
2009	1.66	F	2.68	A+	2.80	A+	2.95	A+	4.00	A+
Year 2009 Western Narrows (m) 1.66 Western Narrows Grade F Eastern Narrows (m) 2.68 Eastern Narrows Grade A+ Western Basin (m) 2.80 Western Basin Grade A+ Central Basin (m) 2.95 Central Basin Grade A+ Eastern Basin (m) 4.00 Eastern Basin Grade A+
2010	1.67	F	2.36	A-	2.94	A+	3.16	A+	3.20	A+
Year 2010 Western Narrows (m) 1.67 Western Narrows Grade F Eastern Narrows (m) 2.36 Eastern Narrows Grade A- Western Basin (m) 2.94 Western Basin Grade A+ Central Basin (m) 3.16 Central Basin Grade A+ Eastern Basin (m) 3.20 Eastern Basin Grade A+
2011	1.29	F	2.18	B	2.36	A	2.51	A	3.07	A+
Year 2011 Western Narrows (m) 1.29 Western Narrows Grade F Eastern Narrows (m) 2.18 Eastern Narrows Grade B Western Basin (m) 2.36 Western Basin Grade A Central Basin (m) 2.51 Central Basin Grade A Eastern Basin (m) 3.07 Eastern Basin Grade A+
2012	1.17	F	2.16	B-	2.47	A	2.85	A+	3.02	A+
Year 2012 Western Narrows (m) 1.17 Western Narrows Grade F Eastern Narrows (m) 2.16 Eastern Narrows Grade B- Western Basin (m) 2.47 Western Basin Grade A Central Basin (m) 2.85 Central Basin Grade A+ Eastern Basin (m) 3.02 Eastern Basin Grade A+
2013	1.31	F	2.44	A	2.51	A	2.47	A	2.94	A+
Year 2013 Western Narrows (m) 1.31 Western Narrows Grade F Eastern Narrows (m) 2.44 Eastern Narrows Grade A Western Basin (m) 2.51 Western Basin Grade A Central Basin (m) 2.47 Central Basin Grade A Eastern Basin (m) 2.94 Eastern Basin Grade A+
2014	1.33	F	2.64	A-	3.43	A+	3.38	A+	3.40	A+
Year 2014 Western Narrows (m) 1.33 Western Narrows Grade F Eastern Narrows (m) 2.64 Eastern Narrows Grade A- Western Basin (m) 3.43 Western Basin Grade A+ Central Basin (m) 3.38 Central Basin Grade A+ Eastern Basin (m) 3.40 Eastern Basin Grade A+
2015	1.36	F	2.44	A-	2.84	A+	3.27	A+	3.46	A+
Year 2015 Western Narrows (m) 1.36 Western Narrows Grade F Eastern Narrows (m) 2.44 Eastern Narrows Grade A- Western Basin (m) 2.84 Western Basin Grade A+ Central Basin (m) 3.27 Central Basin Grade A+ Eastern Basin (m) 3.46 Eastern Basin Grade A+
2016	1.19	F	2.36	A-	2.92	A+	2.86	A+	2.77	A+
Year 2016 Western Narrows (m) 1.19 Western Narrows Grade F Eastern Narrows (m) 2.36 Eastern Narrows Grade A- Western Basin (m) 2.92 Western Basin Grade A+ Central Basin (m) 2.86 Central Basin Grade A+ Eastern Basin (m) 2.77 Eastern Basin Grade A+
2017	1.17	F	2.38	A	2.52	A	2.80	A+	3.20	A+
Year 2017 Western Narrows (m) 1.17 Western Narrows Grade F Eastern Narrows (m) 2.38 Eastern Narrows Grade A Western Basin (m) 2.52 Western Basin Grade A Central Basin (m) 2.80 Central Basin Grade A+ Eastern Basin (m) 3.20 Eastern Basin Grade A+
2018	1.24	F	2.35	B	2.87	A+	3.17	A+	3.14	A+
Year 2018 Western Narrows (m) 1.24 Western Narrows Grade F Eastern Narrows (m) 2.35 Eastern Narrows Grade B Western Basin (m) 2.87 Western Basin Grade A+ Central Basin (m) 3.17 Central Basin Grade A+ Eastern Basin (m) 3.14 Eastern Basin Grade A+
2019	1.23	F	2.45	A	2.77	A+	2.78	A+	3.45	A+
Year 2019 Western Narrows (m) 1.23 Western Narrows Grade F Eastern Narrows (m) 2.45 Eastern Narrows Grade A Western Basin (m) 2.77 Western Basin Grade A+ Central Basin (m) 2.78 Central Basin Grade A+ Eastern Basin (m) 3.45 Eastern Basin Grade A+
2020	1.42	F	2.25	B+	2.51	A	2.70	A+	3.05	A+
Year 2020 Western Narrows (m) 1.42 Western Narrows Grade F Eastern Narrows (m) 2.25 Eastern Narrows Grade B+ Western Basin (m) 2.51 Western Basin Grade A Central Basin (m) 2.70 Central Basin Grade A+ Eastern Basin (m) 3.05 Eastern Basin Grade A+
2021	1.47	F	2.20	B	2.53	A+	2.57	A+	3.41	A+
Year 2021 Western Narrows (m) 1.47 Western Narrows Grade F Eastern Narrows (m) 2.20 Eastern Narrows Grade B Western Basin (m) 2.53 Western Basin Grade A+ Central Basin (m) 2.57 Central Basin Grade A+ Eastern Basin (m) 3.41 Eastern Basin Grade A+
2022	1.40	F	2.65	A+	3.20	A+	3.45	A+	3.67	A+
Year 2022 Western Narrows (m) 1.40 Western Narrows Grade F Eastern Narrows (m) 2.65 Eastern Narrows Grade A+ Western Basin (m) 3.20 Western Basin Grade A+ Central Basin (m) 3.45 Central Basin Grade A+ Eastern Basin (m) 3.67 Eastern Basin Grade A+
2023	1.20	F	2.70	A+	2.90	A+	3.00	A+	3.30	A+
Year 2023 Western Narrows (m) 1.20 Western Narrows Grade F Eastern Narrows (m) 2.70 Eastern Narrows Grade A+ Western Basin (m) 2.90 Western Basin Grade A+ Central Basin (m) 3.00 Central Basin Grade A+ Eastern Basin (m) 3.30 Eastern Basin Grade A+

Focus Question

Is the water clarity improving?

Answer: No, in the open waters of Long Island Sound (where water quality is systematically tracked), water clarity has stayed nearly the same across the Sound since 2008. However, over time there has been an increase in water clarity from west to east in the open waters of Long Island Sound. In 2023, for example, from west to east the average depth of water clarity based on sampling 23 stations, ranged from 1.2 meters (~4 feet) in the Western Narrows to 3.3 meters (~11 feet) in the Eastern Long Island Sound basin. Low water clarity indicates that there may be high phytoplankton abundance (driven by nutrients), sediment, or any other types of suspended particles in the water.

What Was Measured

Routine monitoring of water clarity is done monthly throughout the year and biweekly in the summer by the Connecticut Department of Energy and Environmental Protection (CT DEEP) and the Interstate Environmental Commission. 

Water clarity in the Long Island Sound is measured using a black and white disk called a Secchi disk, which is lowered into the water until you can’t differentiate the black and white quarters of the disk anymore. This level in the water is the Secchi depth and indicates how clear the water is. Water clarity is measured at approximately 23 stations up to 30 times a year.

Status and Trends

Fair

No Change

While water clarity increases from the western to the eastern Sound, individual basins have generally stayed the same throughout the last two decades. High report card scores for water clarity begin just past the Western Narrows, based on the following water clarity depth thresholds (see below). From 2015, the baseline year, water clarity has improved in the Eastern Narrows but remains very poor in the Western Narrows. See Save the Sound’s Sound Health Explorer for basin and embayment grades.

>2.28 m (A- to A+ or 90-100)
2.12 to <2.28 (B- to B+ or 80 to 89)
1.95 to <2.12 (C- to C+ or 70 to 79)
1.8 to <1.95 (D- to D+ or 60 to 69)
0 to < 1.8 (F or <60)

Water clarity is a measure of light penetration into the water of Long Island Sound. Light and light penetration is vital to the Long Island Sound ecosystem, its habitats and wildlife. Water clarity can be decreased by high phytoplankton abundance, sediment, or any other type of suspended particle in the water column. Water clarity can serve as an indicator of the nutrient concentrations in the open Sound, its basins, and embayments. High levels of particulate matter such as that associated with high phytoplankton abundance, also known as algal blooms, are driven by excessive nutrient inputs.