Southland Police are encouraging people to be conscious of the environment they are in after a woman was bitten on the leg by a shark in Riverton.

The 21-year-old was walking in knee-deep water in the estuary, near the Riverton rugby grounds, about 2am on Monday, when she received a significant laceration to her leg that required treatment from emergency services.

The culprit is possibly a sevengill shark, which are present in the estuary.

The time of day is a possible factor.

Riverton is a popular holiday destination, and Police ask that anyone heading into the water follow safety guidelines and avoid late-night swims.