Each season, NCBO scientists compile and analyze data to define whether conditions were average—or whether they differed from average. Then, they discuss what any differences might mean in the NCBO Seasonal Summary. Here are some observations from the Spring 2025 Seasonal Summary. For more information, graphs, and figures, you can access the full scientific document.
Overall, in spring 2025, the Bay saw some small differences from average conditions. For example, salinity was above average for much of the spring. In the Choptank region of Maryland’s Eastern Shore, hypoxia (areas of low dissolved oxygen) was low.
Water Temperature
NOAA satellites track sea surface temperatures. For the Chesapeake Bay, from March through May 2025, water temperatures were slightly cooler than average in the northern Bay, and slightly warmer than average in the southern Bay.
Observations at NOAA CBIBS buoys provide a detailed look at water temperature at several points around the Bay. For example, at the CBIBS Potomac buoy near Point Lookout, water temperatures were below average in early March, above average in early April, below average for a short period of time in late April, and then above average for much of May before once again fluctuating to below average.
Precipitation and Salinity
While the region had experienced low rainfall and precipitation over the winter, spring brought higher rainfall—and thus higher freshwater flow into the Bay. According to precipitation data from NOAA’s National Centers for Environmental Information, rainfall amounts for tidewater Virginia and southern Maryland were the third and fourth highest, respectively, since 2007.
Higher precipitation results in higher freshwater flow to the Bay. This led to declines in salinity toward the end of spring, as observed by the CBIBS buoys, including the station at Annapolis. This is in contrast to spring 2024, when salinity was below average.
While precipitation was relatively high for spring compared to the 2007–2025 mean, the region has experienced drier conditions since fall 2024. Some areas continued to be in moderate drought conditions at the end of spring.
Dissolved Oxygen
The NOAA Chesapeake Bay Office maintains stations that track parameters, including dissolved oxygen (DO) levels, every several meters throughout the water column. Dissolved oxygen (DO) levels at the Lower Choptank and Sharps Island hypoxia monitoring buoys remained mostly within the historical range of values. At Lower Choptank, DO levels remained well above the biological threshold of 4 mg/L. Sharps Island daily averages hovered above or around the historical mean.
What Could These Conditions Mean for Living Resources?
Temperature affects when striped bass spawn. Striped bass typically begin spawning in the spring when water temperatures reach 60°F, with most spawning occurring between 61°F and 69°F. All buoy locations reached 60°F by about mid April, which was a month later than in spring 2024. The spawning season usually lasts from April to mid June.
Once they hatch, striped bass larvae need lots of zooplankton for food. High freshwater flows result in larvae and zooplankton being in the same place at the same time. Striped bass larvae also eat copepods. Cold winter temperatures like we experienced in winter 2025 help slow copepod development. That means that there should be more copepods available in spring when the larvae need them.
However, the sporadic and lower flow observed in winter 2025 and at the beginning of spring 2025 may mean that the juvenile striped bass and the things they eat weren’t in the same places at the same times.
Blue crabs emerge from overwintering burrows at 50°F. All CBIBS buoys crossed above this threshold in the later half of March. Spring’s warmer water temperatures also cue blue crabs to begin reproducing. Blue crabs start spawning at 66°F. All buoy locations reached this temperature in the beginning of May. Surpassing 66°F earlier than usual this spring may have led to spawning starting earlier, and thus a longer blue crab growing season.
Oyster spawning can be triggered at about 60°F; this threshold was met at all buoy locations by about mid April (a month later than in spring 2024). Higher salinity is generally better for oyster reproduction and hatchery operations. Because oysters stay in a fixed location, they are particularly susceptible to hypoxia—they can’t just swim away to find better water. Spring 2025’s relatively low levels of hypoxia bode well for oyster survival.
Salinity is measured in Practical Salinity Units—PSUs. Blue catfish are limited to water with salinity below 14 PSU. Because salinity levels remained above 14 PSU all spring at the mouths of southern Bay rivers like the York and Potomac, blue catfish may have been constrained to upstream, fresher-water areas of those rivers. For more northern tributaries like the Severn River, salinity dropped below 14 PSU in early spring, enabling blue catfish to move more freely.