Hurricane Ida made landfall in Louisiana on Sunday as a major Category 4 hurricane, with winds of 130 knots and an estimated storm surge of as much as 15 feet in the most-affected areas.

The storm is the most powerful to strike the state in many years, and it arrived on the same date that Hurricane Katrina made landfall 16 years ago.

It was downgraded to a Tropical Strom in the early hours of Monday morning.

All ports within the Port of New Orleans captain of the port zone have been closed since Saturday afternoon, except for the port of Venice on the outermost reaches of the Mississippi Delta.

Merchant vessel traffic on the Mississippi has been shut down between Lettsworth, Louisiana (200 miles upriver from New Orleans) and the river's mouth. The Gulf Intracoastal Waterway has also closed in affected areas.

The storm surge briefly caused the mighty Mississippi's flow to reverse, according to data provided by the U.S. Army Corps of Engineers. The river gage at Belle Chase, Louisiana recorded a rapid six-foot spike in the water level and a flow rate of negative 10,700 cubic feet per second at about 1230 hours.

From start to end, the rare phenomenon lasted for about three hours, and it had at least one unusual effect on navigation: the ferry that serves Chalmette, Louisiana broke loose from its moorings and began drifting upstream (not downstream) at mile marker 90, according to local media.