A BLUE-green algae alert at Chaffey Dam, which had been in place for nearly a month, has been lifted.
WaterNSW first implemented a red-alert warning for the area of the dam's storage 30 kilometres south west of Tamworth on February 28.
However, monitoring done by WaterNSW discovered the algae numbers had decreased and the warning was lifted on Tuesday.
A WaterNSW spokesperson said while the region's water supply was safe to drink, anyone who came into contact with the algae should seek medical advice.
"Blue-green algae occur naturally and can reproduce quickly in favourable conditions where there is still or slow-flowing water, abundant sunlight and sufficient levels of nutrients," the spokesperson said.
"Blue-green algae usually appear as green paint-like scums on the water, near the edges, or as greenish clumps throughout the water.
"It makes the water appear dirty, green or discoloured and generally has a strong musty or earthy odour.
"People who believe they may have been affected by blue-green algae are advised to seek medical advice."
A red-alert warning for blue-green algae remains in place for an area of the Namoi River, downstream of Keepit Dam.
Two other red-alert warnings remain in place for areas of Split Rock Dam.
One near the dam wall and the other near the Split Rock recreation area.