A 100kg toddler threw a tantrum after the non-paying swimmer was locked out of the St Clair Hot Salt Water Pool in Dunedin on Saturday.
The critically endangered New Zealand sea lion waddled up the Second Beach track before resting in the shade of the pool's cafe, and was cordoned off from curious onlookers.
Pool supervisor Paul Swanson said the sea lion's nose was pressed up against the automatic doors, ''so we had to turn them off for a bit so that he couldn't come in''.
However, when the shade went, so did the sea lion, straight through two sets of double doors (without paying) in order to lounge by the toddler's pool.
David Agnew, Department of Conservation Coastal Otago conservation services manager, arrived at the pool with a pair of hockey sticks to ''whack together to make a noise'' in order to guide the visitor out of the area.
About 100 people watched and took photos of the sunbathing sea lion, while Mr Agnew and pool staff unbolted a section of fencing so it could get out and return to the sea.
''But he turned and pushed past me and got into the toddler's pool to a big cheer from the crowd.''
The sea lion later decided to upsize pools, forcing staff to evacuate bathers from the area.
The young male then had the 28degC pool to himself for some easy laps.
''But after everyone left he was popping his head up and wondering where everyone had gone.''
About 5pm he exited through the double doors and staff quickly locked the entrance.
''He definitely wanted back in again, he was trying to climb up the doors and pushing hard against them,'' New Zealand Sea Lion Trust trust executive member Shaun McConkey said.
''He didn't give up easily. He was there for around 15 minutes going backwards and forward trying to get into windows and doors and leaving large oily smears.''
The only way to forcibly make him leave would be to sedate him.
''Just try parenting a 100kg 2-year-old having a tantrum''.
Dunedin City Council aquatic services acting manager Nicola Smith, one of three people bracing against the front door as the sea lion tried to force its way back, observed: ''He really wanted back in.''
Staff spent several hours to ensure the pool opened on time yesterday, including chlorinating the pool, which was backwashed and left for 12 hours to filter, and ''we did everything possible to make it clean''.
Mr McConkey said the sea lion was not microchipped and was believed to be from Stewart Island or Auckland Island. Sea lions were very sociable and would often try to interact with humans, ''so he may well be back,'' he said.
Mr McConkey recommended a barrier be erected along the track to prevent repeat sea lion visits. Their South Island population numbers about 200.
The sea lion was last seen waddling back along the Second Beach track.
Sources confirmed he did not pay the $1 casual entry free for under-5s.
