The Chesapeake Bay in 2018

A Year in Graphs

Weather Trends

This BayData product from the Virginia Institute of Marine Science summarizes how physical conditions impacted the health of the Chesapeake Bay during 2018. Mouse over any data graphic to reveal its interactive features.


2018 was an unusually wet year throughout the Chesapeake Bay watershed

Several bouts of heavy rain—particularly in May and late June—combined with consistent background precipitation to make 2018 one of the wettest years on record at localities around the Chesapeake Bay, including Richmond, Virginia (shown here); Baltimore, Maryland; and Harrisburg, Pennsylvania. All data are from weather stations operated by NOAA's State Climatology Network.

Ample freshwater runoff helped drive Chesapeake Bay salinity to abnormally low levels

A rainy May swelled tributaries throughout the Chesapeake Bay watershed, bringing record levels of freshwater runoff into the mainstem Bay. Continued above-average rainfall and runoff through the summer and fall kept salinity below historical norms until year's end. Available data were compiled by Erin Shields from the Gloucester Point (GP) Continuous Monitoring Station (YRK005.40) part of the VECOS network operated by the Chesapeake Bay National Estuarine Research Reserve at VIMS.

Air temperatures rode a roller coaster across the Chesapeake Bay watershed

A generally chilly start and end to 2018—as shown here in Williamsburg, Virginia—was punctuated by abnormal warmth in January, February, and late summer. The September warm spell was particularly bad news for eelgrasses in the Chesapeake Bay. To discover how 2018 temperatures in Williamsburg compared to normal and record highs and lows for each day, view this graph. All data are from NOAA's State Climatology Network. Williamsburg is of course just a single location, at the whims of local weather. To see how 2018 compared to previous years on a global basis, visit NOAA's Climate Prediction Center. Preliminary global data suggest that 2018 was the 4th warmest year on record, after 2016, 2015, and 2017.

Heavy rains and low salinity had big impacts on the Bay and its marine life

Oysters & Dermo

Low salinities harmed some oysters but kept Dermo disease at bay

Dermo is inhibited by reduced salinity, and during our fall 2018 survey we found that the percentage of oysters infected by Dermo was below average in all but 1 of our 26 sampling sites. Indeed, 2018 set a record low for average disease prevalence across sites. Oysters themselves were also challenged by the very low salinities, with some mortality at upstream locations. Those that survived, however, are benefitting from reduced Dermo disease pressure, which should last into 2019." —Dr. Ryan Carnegie, Shellfish Pathology

Low salinity and a warm September was bad news for some baygrasses

"An on-the-ground assessment of areas along the Bay's western shore in late September revealed that almost all the eelgrass had defoliated, leaving many areas normally vegetated in the fall completely barren. We think the low salinity, high turbidity, and warm temperatures triggered this massive defoliation."—Dr. Robert "JJ" Orth, Seagrass Monitoring & Restoration
Low-Oxygen Dead Zones

Stormy weather in mid-summer mixed oxygen into previously hypoxic waters

"One might think that the reduction in surface salinity could increase stratification, and hence increase hypoxia. But the storminess that accompanied the precipitation has actually caused increased mixing and almost completely eliminated hypoxia in late July."—Dr. Marjy Friedrichs, Biogeochemical Circulation Ocean Modeling