Police are requesting help from the public to ascertain whether a swimmer has safely made it out of a river after jumping off a bridge on Friday.

A search for a swimmer in Cambridge resumes on Saturday afternoon, but Police want to hear from a couple who may have seen the man leave the water.

Police were alerted to a possible missing swimmer about 5.30pm on Friday.

"The man had jumped off the Low Level bridge on Shakespeare Street, near Tirau Road, but it is not known if he made it out of the water," says a police spokespersn.

"It is possible that a couple near the boat ramp may have seen the man come out of the river."

Police would like to speak to the couple to establish if that is the case.

"If you were witness to this incident or have dash camera footage of the area at the time, please contact Police immediately and quote job number P057410928," says a police spokesperson.