The Science of Mean Lower Low Water (MLLW)
We report in Mean Lower Low Water (MLLW), a specific tidal datum used as the zero-elevation reference for nautical charts in the United States. MLLW is defined as the arithmetic mean of the lower of the two daily low tides recorded at a tide station. This average is calculated from data collected over a specific period known as a National Tidal Datum Epoch (NTDE).
Hydronet provides real-time environmental data collected from various sensors and partner networks. Please note that the data is automatically transmitted and may contain occasional errors, gaps, or anomalies due to equipment malfunction, communication issues, or maintenance activities. Hydronet data is provided for informational and research purposes only and should not be considered authoritative or used for emergency decision-making.
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.
