Read the full scientific Winter 2025–26 Seasonal Summary.
With extended periods of air temperatures below freezing leading to significant areas of the Chesapeake Bay icing over, this past winter is one we’ll remember for a while! The colder-than-average water, low freshwater flow, higher-than-average salinity, and higher-than-average dissolved oxygen that were observed at locations around the Bay could have notable effects on the Bay’s living resources.
Data from NOAA satellites shows that overall for December 2025–February 2026, water temperatures were below average throughout the Bay and out into the Atlantic Ocean.
A map developed from satellite data shows the Chesapeake Bay colder than average over winter 2025–26.
NOAA’s CBIBS buoys were affected by the cold: The two northernmost buoys were removed from the water in advance of frigid temperatures in January to keep them safe from ice damage; other buoys stopped reporting due to icing conditions. The CBIBS buoy off York Spit was the lone station to track conditions throughout the challenging winter. York Spit registered temperatures for the final 5 weeks of winter that were 6.5°F lower than previously recorded by this station for that period.
Water temperature at the CBIBS York Spit buoy, shown in this graph, was colder than average for much of winter 2025–26.
York Spit’s complete data record for December through February also shows that salinity was several PSU higher than average for much of the winter. On many days, salinity at York Spit was higher than any value recorded for the same date since the buoy was deployed in 2016.
Salinity at the CBIBS York Spit buoy was markedly above average throughout winter 2025–26, as demonstrated in this graph.
Lower-than-average rainfall amounts, leading to less freshwater flow into the Bay, were the root of this higher-than-average salinity. Rainfall in southern Maryland was the fifth lowest since 2007.
Areas in the Chesapeake Bay watershed received less rainfall than average. This graph shows that in southern Maryland, winter 2026 precipitation was well below average.
Toward the end of February, several rainfall events increased flow at locations around the Bay including in the Choptank River. Analysis in the Spring 2026 Seasonal Summary will indicate whether this increase in freshwater input was enough to decrease salinity.
Data displayed in this graph show that streamflow was well below average for much of winter 2025–26.
The NOAA Chesapeake Bay Office was able to deploy a dissolved oxygen (DO) monitoring buoy at the Sharps Island station (located in the Chesapeake Bay Program’s monitoring segment CB4MH) in the mainstem of the Bay in early January. For many species, DO indicates habitat quality: DO below 4 mg/L is poor habitat quality, and higher DO is better habitat quality. The Sharps Island station observed higher than historical DO averages for February at all depths and was at historic high values for dissolved oxygen at 13 and 15 m.
A hypoxia monitoring station was deployed off Sharps Island in mid-January. It tracked higher-than-average DO for the rest of the winter.
Effects on Key Species
These graphs and visualizations show a complex blend of conditions. What do colder water, higher salinity, lower freshwater flow, and higher DO mean for key species in the Chesapeake?
Striped Bass
The colder waters could help the 2026 spring striped bass spawn. Studies show that colder winters are often followed by a successful striped bass spawning year. This could be because of reduced predator activity (white perch and possibly blue catfish) in the colder water. It could also be that the colder water sets up a better timing match with zooplankton (food for striped bass larvae) being available when larvae hatch in the spring.
The low freshwater flow this winter sets up two potential outcomes for striped bass. On one hand, the higher salinity could help striped bass, because their eggs need to stay suspended in the water column to hatch. Higher salinity increases water density, which helps eggs stay afloat rather than sink. On the other hand, if low flow persists into spring, it could diminish spawning area in places where striped bass spawn, including the Choptank and Potomac rivers. This could be buffered by moderate spring rains, which could create better salinity and flow conditions.
Menhaden
The severe cold snaps in January 2026 prompted many resident menhaden to start their southward migration earlier than usual. Menhaden may have left the upper Bay more quickly than their predators (like striped bass), leaving less for the predators to eat, at least temporarily. The higher salinity may be good for the future of menhaden, because juvenile menhaden often survive better in higher-salinity environments.
Blue Crabs
Blue crabs also likely saw some benefits—but some drawbacks—in winter conditions. Blue crabs spend the winter burrowed in the mud. When bottom temperatures in the Bay drop below 38.1°F, more crabs die. So this winter’s cold water temperatures were likely bad for blue crabs’ survival, particularly for adult females and juveniles.
But while the cold was a threat, the higher salinity levels may have helped the crabs. In very fresh, freezing water, blue crabs’ internal salt balance fails, which leads to death. This winter’s higher salinity may have buffered some of the crabs from the extreme cold snaps. Also, having saltier water near the mouth of the Bay helps blue crab larvae and juveniles entering the estuary.
Oysters
This winter’s conditions were a mixed bag for oysters, too. Colder temperatures can kill intertidal oysters—oysters that live between the high and low tide lines. But the higher salinity meant oysters weren’t stressed by “freshening” events, which can cause mass die-offs if salinity drops below 5 PSU for extended periods.
La Niña
The Fall 2025 Seasonal Summary noted that a weak La Niña was beginning to form and was expected to persist through the winter. For the Chesapeake Bay, La Niña conditions often bring above-normal temperatures but also increased sharp cold snaps and shifts in salinity.
December 2025 and January 2026 did indeed bring periods of intense cold and arctic air spills to the Chesapeake. But the weak La Niña began to collapse earlier than expected, transitioning toward neutral conditions by late February and March 2026.