Updated 8/10/2012 at 4 p.m.

EVANSTON, Ill. (CBS) — Dangerous conditions on Lake Michigan prompted Evanston to close its public beaches.

People can still go to the beach, but cannot go into the water, city officials said, citing 10- to 14-foot waves and safety concerns. The city has six beaches; a seventh is located at Northwestern University.

The National Weather Service says waves on the lake could become as high as 21 feet. Waterspouts and rip currents also are possible.

LISTEN: WBBM Newsradio’s John Cody reports

A rip current hazard warning is in effect through Saturday evening, and a gale warning is in effect until 9 p.m. Friday.

CBS 2’s Susanna Song reports the winds were gusty at the North Avenue Beach late Friday morning, and the waves were crashing violently.

At the lifeguard station, a red flag was posted, signifying that swimming has been banned. Boats and jet skis have been put away.

Some paddleboaters were outmaneuvering the high waves off Greenwood Beach in Evanston, but unless you are a highly experienced boater, such activities are not advised.

The U.S. Coast Guard and the Police and Fire departments are concerned about people being caught in a rip current.

“Big waves, and then there’s a rip current warning that’s been issued,” said Chicago Fire Department Chief Ron Dorneker, “and then remember with a rip current – a rip current doesn’t take you down to the bottom. It just takes you up, so it pulls you away from the shoreline. What we recommend with a rip current is you swim parallel to shore, because eventually, that force of the water is going to subside, and you’re going to be able to swim back to shore. So never try to swim against that current.”

But some people like wind and crashing waves – provided that they don’t go up too far on land.

“This is my favorite time to be out, because I love the wind and the roughness; I don’t know, I really like it,” said Debra Heinrichs, “(but) not in the water, no, not when it’s like this. I sometimes dream or riding my bike out to the edge of the pier.”

Further advice if you’re caught in a rip current is just to relax and not to panic, kick your legs, and again, swim parallel to the beach.

And what exactly are rip currents? AccuWeather meteorologist Alex Sosnowski tells WBBM Newsradio’s John Cody that they’re pretty much water trying to get back where it came from.

“They’re pushing water toward the coast. It has to escape somewhere, and it tends to do that in narrow channels,” Sosnowski said, “so the stronger the wind is pushing the water on shore, the more significant the number and strength of these rip currents can be.

Sosnowski says the tip off for rip current conditions are strong winds blowing onto shore, high waves, and brown or sandy colored water showing turbulence scouring the lake bottom – all signs to be alert for rip currents carrying water, and possibly swimmers. off short.

Conditions are also unsafe for boaters. A gale warning is in place until 9 p.m. for the entirety of the shoreline from Winthrop Harbor near the Wisconsin state line to Michigan City, Ind.

For boaters, a gale warning means winds of 34 to 47 knots occurring or expected. No one without the proper experience and equipment should operate a boat in such conditions, the National Weather Service warns.

The high winds also pose a risk for waterspouts – funnels that behave like weak tornadoes on the surface of the lake.

The National Oceanic and Atmospheric Administration advises that anyone out on the lake who sees a waterspout should move at a 90-degree angle to its apparent direction of movement.

And just because the Eensy Weensy Spider went up the waterspout doesn’t mean you should do it too. All jokes aside, NOAA advises that you should never approach a waterspout to investigate, because they can be as dangerous as tornadoes.

The high for the day Friday is only 74, and conditions will remain cloudy and windy, reports CBS 2 Meteorologist Mary Kay Kleist. Sunny and pleasant conditions return for Saturday, when the high is 78; and Sunday, when the high will be 79.

The high for Monday is 77, Tuesday 84, Wednesday 87 and Thursday 88.