Water Level Reference
What does “ft MLLW” mean?
Hydronet reports water level relative to Mean Lower Low Water, or MLLW. MLLW is a local tidal reference based on the average of the lower low tides observed over a long-term tidal period.
When a station shows 1.83 ft MLLW, that means the water surface is approximately 1.83 feet above that station’s MLLW reference level.
How high the water is compared with the local tidal reference level at that station.
It is not water depth, ground elevation, or NAVD88 without a datum conversion.
A consistent tidal reference helps show how water levels change over time.
Help Improve Hydronet Flood Monitoring
Help improve Hydronet’s flood monitoring system by reporting local flooding near our sea level sensors. Use this form to record when and where flooding begins. Your input will help us develop a region-specific alert system for coastal communities.
Questions about Hydronet?
For questions about Hydronet, data access, partnerships, or site coordination, please contact the Hydronet team at hydronet@umd.edu.
Data Use Disclaimer
Hydronet data are provided for informational and research purposes. Data may be preliminary and subject to review, correction, or outages. Users should exercise judgment when interpreting water level observations and should not rely on Hydronet as the sole source for emergency decision-making.
