Surf Lifesaving Otago volunteers reported a peak of about 100 people in the water at St Clair and 50 to 60 at St Kilda, with hundreds more basking on the sand.
Bathers observed beach safety rules and, apart from some minor rescues, there were few concerns.
At Outram Glen, more than 200 bathers were at the Taieri River above and below the Outram bridge.
Inland Otago temperatures were generally in the high 20s, with Alexandra posting 30degC at 3pm.
Swimmers were attracted to Lake Dunstan and shallow, slow-moving parts of the Clutha River, near Millers Flat.
But Dunedin hydrologist Dave Stewart warned a westerly trough could lead to unsettled weather, with late showers on New Year's Eve over western areas of Otago.
The timing of rain over the rest of Otago would depend on when the associated front moved through.
