Flood gates were installed Sunday along a section of the Missouri River in Omaha to keep rising water from seeping into downtown, city officials said.

Officials in Nebraska and Iowa have been monitoring the river, which is expected to crest near Omaha at record levels between 30 and 35 feet in late June after more water is released from reservoirs in North Dakota and South Dakota. The U.S. Army Corps of Engineers measured the river at 28.8 feet Sunday in Omaha. Flood stage is 29 feet.

Water has already spilled over the banks in several low-lying areas along the river in Nebraska and Iowa. That means more than 1,000 acres of farmland in southeast Nebraska has flooded, and water is encroaching on cities such as Fort Calhoun, Neb., and Sloan, Iowa. Last week, Omaha closed one city park along the Missouri.

The city also announced Sunday that it was closing isolation gates at the Monroe Street Lift Station, a move that will allow the release of some untreated wastewater into the river. The Public Works department urged people to avoid wading or swimming in the river near the Veterans Memorial Bridge in south Omaha and for several miles downstream until further notice.

The corps predicts that 2011 could be one of the wettest years on record in the Missouri River basin. Officials are predicting record river flows and large releases from upstream reservoirs because of steady spring rain and above-normal snowpack.

The corps warns that the high water level and flooding issues will likely worsen over the next month as releases from upstream reservoirs reach historic levels.

In South Dakota, the surging river is expected to jeopardize hundreds of homes and businesses in low-lying areas of Pierre and Fort Pierre. Officials said Sunday that emergency earthen levees already under construction will be built another 2 feet higher in an attempt to protect property. Residents further downstream in Yankton and Dakota Dunes were also warned about flooding and possible evacuations.

North Dakota also is bracing for the increased Missouri River releases, but the corps said construction of more than seven miles of earthen levees to protect against flooding in Bismarck and Mandan should be completed long before planned maximum releases at the Garrison Dam.