Just before 6 p.m., a man went into the water at Hammel Woods and quickly began having trouble, a witness told the Will County Forest Preserve police.
The man's girlfriend began yelling to get the attention of a witness and a Will County Forest Preserve police officer.
The woman also went into the water.
Chief Tracy Chapman says according to the witness, they were not on a boat.
The two are presumed dead. Crews were conducting a recovery mission, officials said Sunday night.
The witness described the victims as possibly being in their 20s.
Shorewood police will hold a press conference at 10 a.m. Monday.