Nelson City Council continues to monitor a deadly algae in a local waterway.

Levels of the cyanobacteria algae are up in the Maitai River, due to a lack of rain.

Nelson City Council is warning it could be fatal to dogs, which might eat it when they're playing in the water.

It's put up warning signs and is urging dog owners are to take their pooches swimming in the permitted area at Tahunanui Beach.

It says as it's a naturally occurring bacterium there is little that can be done to remove it, apart from waiting for the river to be cleared naturally by rain.

However there is no significant rainfall forecast for the coming week.