The water level in Lake Ontario hit a modern-day high on Friday, exceeding by a sliver the record set just two years ago.

The preliminary calculation for Friday showed the lake at 248.98 feet above sea level. That surpassed the record of 248.95 feet, which was reached on four different days in late May 2017.

Even in calm water, the record high water has inundated some low-lying properties. But the worst flooding occurs when winds generate larger waves that over-top and destroy shoreline protective structures and flood adjoining property.

More:Flood watch upgraded to flood warning for Sunday evening along Lake Ontario

When the lake hit then-unprecedented highs in the spring and summer of 2017, a string of wind-and-wave events caused the worst sustained shoreline flooding in modern history. Thousands of residential and commercial properties on both sides of the lake, in New York and the Canadian province of Ontario, suffered some amount of damage.

No official damage total was calculated, but it likely was $200 million or more.

This spring, winds and waves again are wreaking havoc. The worst event so far occurred Tuesday when northeast winds generated waves of two to three feet.

The National Weather Service has cautioned that larger waves will strike parts of the shoreline Sunday, Monday and Tuesday.

How much longer the lake level will continue to rise is largely dependent on how much rain falls in coming days and how much water regulators are able to release through a dam on the St. Lawrence River.

The outflow through the dam was increased by about two percent early Friday, the ninth such jump since mid-May.

If precipitation stays near “normal” and outflows through the dam continue to be stepped up, the lake should rise to about 249.07 feet and peak in the next week or so, said Keith Koralewski, a hydraulic engineer for the U.S. Army Corps of Engineers who advises the lake-level regulators.

The daily water level that held the record until two years ago, 248.75 feet, was set in June 1952, before the control dam on the St. Lawrence was built. Lake-level records go back to 1860.

The lake level is calculated daily by averaging hourly readings from government-run gauges at Oswego, Rochester and Port Weller, Ontario on the south shore, and Toronto, Cobourg and Kingston, Ontario on the north shore.

SORR@Gannett.com