What are those balls in the Gowanus Canal?

There’s something floating atop the notoriously polluted Gowanus Canal — and it’s actually a good thing!

The Department of Environmental Protection said that those new red and white buoys dancing on the greasy waterway’s surface are a colorful warning for vessels not to damage newly installed pipes that are suspended underneath, part of a multi-million initiative to improve water quality and reduce the canal’s trademark stink by mixing oxygen with canal water.

The temporary system will oxygenate the water during the $50-million rehabilitation of an existing flushing tunnel and a $85-million upgrade of the wastewater pumping station, both of which will be done by 2013.

During those upgrades, the flushing tunnel will be turned off, necessitating the aeration piping.

The temporary system will be up and running in August, the city said. The work is proceeding independently of a federally led Superfund clean-up of the canal.