Witnesses said five people were struggling in the water along the riverwalk about 10:45 a.m.
All of them were between the ages of 15 and 18.
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Four of them are out of the water, one is in critical condition. The other three are in good condition.
U.S. Coast Guard and Department of Natural Resources officials are continuing to search for a 16-year-old from Chicago.
Authorities said high winds and rip currents played a role in the incident but did not provide any information about the genders or identities of those involved.