David Yoon, 9, visiting from Toronto, was disappointed he couldn't test Q's swimming abilities. (Michal Roberge/CBC)

Talk about a quick dip.

One day after a city-sponsored party, two Halifax harbour beaches were closed to swimmers pending the results of new water quality tests.

Municipal officials shut down Black Rock Beach and Dingle Tower Beach on Sunday because of heavy rains and fears that bacteria levels had risen.

Officials said this was a precautionary move after Saturday night's rain, not a result of unsatisfactory water tests, even though a sign posted at Black Rock in Point Pleasant Park cites high bacteria counts.

James Campbell, spokesman for the Harbour Solutions project, said heavy rain in a short period of time can overwhelm the sewage system, and the chamber that collects sewage and stormwater can overflow.

"When that happens some screened raw sewage can be discharged into the harbour and in that event rather than be sorry — to be safe — we shut down the beaches," he said Tuesday.

Campbell expects to get the results of water quality tests by Wednesday afternoon. In the meantime, swimmers are banned from Black Rock Beach and Dingle Tower Beach.

Gillian Nauss was among the would-be swimmers turned away Tuesday from Black Rock.

"It's confusing because just two days ago they said we could swim and now they're saying we can't swim, so it's disappointing," said Nauss, who planned to take 20-month-old son Ethan for a dip.

David Yoon, 9, visiting with his family from Toronto, wanted to swim with his dog, Q.

"I wanted to see if my dog can swim because we've never seen her swim before," said Yoon. "The lifeguard said the bacteria levels are high and my mom said 'no.'"

Some hardy swimmers joined municipal politicians on Saturday for an official beach party.

Bacteria levels have dropped since the $333-million Harbour Solutions sewage treatment project got underway, prompting the return of lifeguard chairs for the first time in 30 years.

The municipality also hired divers to pick up some of the junk, shopping carts and beer kegs that used to line the bottom.