Saturday morning, the New River was as still as glass. Usually you can see the tide flowing in or out - here's tide chart. The tide moves very quickly and the difference between high and low tide shows very clearly in the height of the docked boats or the water covering the cement access stairs.
The New River flows into the Intracoastal Waterway, and from there into the Atlantic Ocean. Sometimes you can see a manatee or bull shark, especially if you look down from the 19th floor of our building. The water is quite clear.
The geology of the New River is unique, because it is not truly a "river." The river is not draining fresh water: it is completely tidal saltwater. On a rising tide, the current flows upstream, as far as five miles inland. Twelve thousand years ago, the lower Florida peninsula was a vast atoll, bordered by a coral reef on the eastern side. The New River was actually cut by the tidal flow between what is now the Everglades and the Gulf Stream. As the earth cooled and ocean levels receded, this pass through the coral reef became this unusual river.
Because the river is cut deep into coral rock, it does not silt up, and does not pose the usual threats of shifting sand bars. The depths of the river do not change.
It is very deep, up to 60 feet in places with a minimum draft of 12 feet. It's not unusual to see 150 footers making their way up to the big yacht yards. It also has a few treacherously tight bends, so most of the huge yachts make use of tug escorts to stay safely in the deepest portion of the channel.