This region of the Patuxent River is 45 miles upriver from the Chesapeake Bay, yet the waters of Jug Bay are tidal. The tides cause waters to rise and fall throughout the day. The marshes here are called freshwater tidal wetlands.
The tides are caused by the gravitational pull of the moon and the sun on the world's oceans and estuaries. The Chesapeake Bay tides are called semi-diurnal tides. That is, in a 24-hour period the two high tides are of unequal height, as are the lows. The relative positions of the moon and sun in relation to the earth cause variation in the heights of consecutive high and low tides throughout the month. During the new and full moon we experience the greatest tidal amplitude. These conditions occur when the earth, moon and sun are more or less in line. These are the "spring" tides, although "spring" tides occur every month of the year and not just in the spring. Twice each month the moon is at a right angle to the earth-sun axis. At these times, we experience neap tides or the tides with the least amplitude. Every month we have two spring tide and two neap tide periods.
The Patuxent River estuary usually has two high tides and two low tides every day. High and low tides are four to six hours apart. Average tidal amplitude, which is the difference in height between high water and low water, is about 0.5 meters or 18 inches. Maximum tidal amplitude at Jug Bay is about 1 meter. The tides advance by about 50 minutes each day: if it is high tide today at noon, tomorrow's high tide will be at about 12:50. This is approximate.
Strong winds associated with coastal storms, as well as heavy rains, can dramatically augment the "table" tide heights in the Patuxent River estuary. Winds out of the north or northwest can blow water out of Jug Bay exposing bare mudflats, whereas heavy rains in the upper watershed can cause flooding that make the marshes and river look like a large lake. Additionally, releases of high water from the two reservoirs in Howard County can cause the river to rise rapidly, especially in the narrow channel upstream from Wayson's Corner.
Boaters, kayakers, and canoe paddlers, as well as those conducting research or field trips on foot into the tidal marshes, should check the tide table before planning activities. Paddlers attempting to return to shallow launching sites during low tide conditions might be unable to reach shore or could even become stranded in the barely-exposed mud. The two hours before and after high tide usually make for the best paddling conditions. Consult your tide table!