Highlights from our 2021 Annual Water-Quality Report

[Note that due to the many variables that affect water quality, significant trends in water quality are not always evident when looking at a single sampling season’s data. Rather, statistically meaningful trends normally become evident only after sampling occurs over many seasons during a variety of conditions. In some cases, the data in the 2021 annual report compare parameters (such as rainfall and bacteria levels) that show expected correlations but in other cases, they display noticeable variability}. Here are some of the highlights. The full report can be found on our website under Documents.


• Levels for fecal indicator bacteria were lower at outer-harbor stations than near-shore and outfall stations, likely because they are less influenced by stormwater and other discharges from the watershed.

• Samples tested for fecal indicator bacteria at stations in Glen Cove Creek had levels that consistently exceeded the beach closure thresholds toward the end of the season and were later discovered to be related to a sewer line break.

• The outfall for the powerhouse drain had consistently high levels of bacteria for samples taken directly from the discharge.
• Results from both summer and winter monitoring at Scudder’s Pond have shown lower bacteria levels for both fecal coliform and enterococci as compared with pre-restoration levels.
• Hempstead Harbor beaches were closed due to high bacteria levels for 11 days during the season.


• Healthy DO levels (greater than 4.8 ppm) were observed in 79.3% of all surface and bottom measurements taken in 2021, compared with 83.8% in 2020.

• For bottom DO levels (which are most crucial to bottom-dwelling marine life), hypoxic conditions (less than 3.0 ppm) were observed in 9.1% of all measurements taken in 2021, a slight improvement over conditions observed in 2020.

• Hypoxic conditions were observed in none of the surface readings for the 2021 season.

• In 2021, there were no anoxic readings (less than 1.0 ppm).

• Hypoxic conditions occurred from the third week of July through early September, but at most stations, hypoxic conditions subsided by mid-August, a slightly shorter period than that observed in 2020.

• Hypoxic conditions were observed at stations CSHH #1-2, #4, #6-7, #15, and #16-17.

• Station CSHH #7 had the highest percentage of hypoxic readings for bottom DO levels in 2021 at 29%.

• The period of hypoxic conditions was shorter in 2021 than in 2020.


• The average bottom water temperature for the 2021 season was 20.42 deg. C.

• Unusual cooler surface temperatures occurred on September 3, 2021, likely due to heavy rainfall from Hurricane Ida.

• The average surface water temperature for the 2021 season was 20.91 deg. C.


• The average salinity in Hempstead Harbor was 2.34% lower in 2021 than in 2020.

• In 2021, Tropical Storm Elsa and Hurricanes Henri and Ida resulted in significant local rain events with notable impacts on salinity.

• Near-shore stations show stronger correlations between rainfall and average salinity than other stations, and in 2021, the changes in salinity at near-shore stations could be explained to a large extent by the amount of rainfall within 48 hours of sampling.

• The highest salinity recorded in 2021 was 27.15 ppm (bottom CSHH #16 on June 30), and the lowest was 14.23 (surface CSHH #7 on September 3)—exhibiting a larger range than seen in previous years.

pH –

• Average pH levels in Hempstead Harbor in 2021 were 7.77 at the surface and 7.64 at the bottom.

• Average surface and bottom pH levels in 2021 were comparable with long-term averages (2005-2021).

• The lowest (7.15) and highest (8.43) pH measurements for the season were recorded at CSHH #16.


• The average Secchi-disk depth for the 2021 season was 9.9% deeper than the 2020 average.

• Unusually clear water conditions occurred on June 2, 2021.

• The highest average turbidity measurements, for both surface and bottom, occurred at CSHH #7.
• Stations in the lower harbor and ones closer to the shore tend to have higher turbidity, while stations in the outer harbor tend to have lower turbidity. This is reflected in the 2021 data.

• In 2021, average total nitrogen was highest at outfall stations (CSHH #14A, #15A, and #8).

• In 2021, average total nitrogen ranged from 1.0 mg/L to 5.3 mg/L, while in 2020, average total nitrogen ranged from 0.41 mg/L to 5.8 mg/L.

• CSHH #8 had the highest average ammonia levels of all stations sampled; for each sampling date for the entire season, total nitrogen consisted of up to 66% ammonia.
• All stations tested in 2021 had at least one reading over the course of the season that exceeded the 1.2 mg/L total nitrogen threshold, considered very poor.

• The average total nitrogen for all but one station exceeded 1.2 mg/L, considered very poor quality.


• The numbers for many of the fish caught in Hempstead Harbor seines were up from 2013 (the year that the power plant substation that was located along the shore of the lower harbor was dismantled; see the previous section on the Glenwood power station monitoring report). Most significantly, the Atlantic menhaden (young of the year), which were not included in the 2013 seine catch, were up to a stunning count of 203,932 in 2015. In 2017-2019, the “bunker” totals were 12,086, 3,165, and 1,386, respectively; in 2021, the total was up to 7,815. (Note that in 2020, no seining was conducted in May and June because of COVID-19 delays; therefore, total catches and the number of species represented for the entire season are reduced compared with other years’ seasonal totals.)

• Significant seine catches in Hempstead Harbor for 2021 included bluefish (643), northern puffers (274), scup (aka porgies) (9,139), silversides (16,961), and killifish (786). Also of note, the number of blue crabs (61) was up significantly from previous years and corresponds with our monitoring observations.

• For commercial shellfish landings, the 2021 haul was down from the previous year, but still substantial, at 11,111 bushels of hard clams. The soft-shell clam haul increased to 12 bushels, and the oyster haul was a third of what it was in the prior year.

• In October 2021, HHPC contracted with Cashin Associates to conduct a shellfish density survey for Hempstead Harbor. The survey included 183 samples that were collected from stations throughout the harbor and were consistent with those used for the 2008 and 2013 surveys. The final survey report (issued on April 13, 2022) concluded that, overall, clam density had increased, with the highest number of clams per square meter in the lower harbor. The percent of seed clams by population was still very low compared with the 2008 finding, mean size of clams had also increased, overall indicating an older and therefore unstable clam population. No oysters were obtained in grab samples, although some were observed by divers who assessed the harbor bottom to create a sediment survey map.

• On January 17, 2021, large bunkers were observed swimming at the head of the creek at the dogleg section that spills out from Mill Pond. Several dead fish were on the rocks below the spillway, seemingly left as the tide went down. Freezing temperatures likely contributed to this bunker mortality.

• In February, a resident photographed Hempstead Harbor’s resident bald eagles in a snowy perch in Roslyn Harbor and reported that at the end of the month they had been observed mating. He also reported seeing a few red foxes in Roslyn Harbor, all looking in good health.

• By March 26, the ospreys had returned. Two new osprey nests were spotted around the harbor—one built precariously on top of a crane at Gladsky Marine Salvage in Glenwood Landing and another on the dock house of the Sea Cliff Yacht Club. There are 15 visible osprey nests along the harbor.

• In mid-May, we received reports of jellyfish in the harbor that seemed to have a red dot on them and other reports of clear jellies in the water off Sea Cliff beach. On May 19, we saw more than 40 small jellyfish carried quickly out of the lower harbor on an outgoing tide. Although they had some similarities to lion’s mane jellies that we have seen previously in Hempstead Harbor, there were several differences. The top of the bell was a deep orange-brown color in the center surrounded by a lighter orange color with a dark fringe, and there were no apparent long tentacles trailing from the underside of the bell. Kim McKown of NYS Department of Environmental Conservation, Marine Resources, and others helped with identifying them as early stages of lion’s mane jellies, which can also be clear—as seemed to be the case with the jellies seen off Sea Cliff Beach at about the same time in May.

• On June 2, we saw large comb jellies (sea walnuts), too numerous to count, in Tappen Marina. The following week, only two sea walnuts were observed near Beacon 11.

• On June 8, a resident reported observing two fledglings in the bald eagle nest in Roslyn Harbor. He also reported seeing two red foxes with two kits and many goslings and groundhogs in the area. At this point, we had not seen the youngest members of the bald eagle family, but we did observe two adults on June 23 during the monitoring trip to the lower harbor.

• On July 5, we received reports of dolphins in Oyster Bay. The next day, a pod of about 50 dolphins was seen in Hempstead Harbor near the Legend Yacht & Beach Club (the former Lowe estate) in Glen Cove at about 3 pm. During the next day’s monitoring survey, we noticed more bunker activity at the surface throughout the harbor, which may have attracted the dolphins.

• Throughout July, we saw the usual variety of birds: cormorants, mallard ducks, great egrets, a few snowy egrets, Canada geese, great blue herons (up to 12 on one day), one hooded gull, ospreys, swans, and terns. In early July, we saw one turkey vulture flying over Glen Cove Creek. On July 21, we saw one belted kingfisher, 3 killdeer, and 3 tiny piper types (possibly sanderlings). On the two trips to the lower harbor during June, we saw two adult bald eagles; on the second trip, we had our first sighting for the season of two juvenile bald eagles.

• On August 11, we noticed about 30-40 dead bunker floating by as we traveled to our monitoring stations. Most were very large and in varying states of decomposition. We also noticed about a dozen dead bunker on docks in Glen Cove Creek—brought up and eaten by birds. There have been large schools of bunker throughout the harbor. We saw large schools of bait fish and numerous blue crabs that seem to be unaffected by whatever was affecting the bunker. We did see a very large dead carp in Glen Cove Creek on August 11 (we’ve noted previously that some carp evidently make their way from Mill Pond and end up at the head of Glen Cove Creek, but this one was closer to the mouth of the creek, following an outgoing tide).

• In September there were coyote sightings in the Roslyn Harbor and Glenwood Landing areas.

• On October 6, a peregrine falcon was perched on the Gladsky Marine crane that has been a fixture in the lower harbor for years.

• On November 23, we received a report that an Atlantic right whale was spotted near the Throgs Neck Bridge. Bunker were present in Glen Cove Creek into December. On December 8, bunker were seen finning near the Glen Cove STP outfall, some swimming sideways, and some had copepods and algae attached to them.

Leave a Reply