Toxic algal bloom closes once pristine lake

Lake Clearwater in Ashburton Basin lakes is closed as of yesterday until further notice due to terrible water quality from a potentially toxic algal bloom.

The algal bloom is caused by increased nitrogen and phosphorus levels in the catchment. Canterbury District Health Board press release here.

Land use intensification of sheep and beef farming over the past 10 years is taking a toll on biodiversity and recreation for Lake Clearwater and neighbouring lakes and wetlands. The area is normally known for wildlife like Australasian crested grebes and secretive wetland birds like bitterns, as well as recreational fishing, boating, and windsurfing.

Debs Martin, Forest & Bird Regional Conservation Manager, was at Lake Clearwater this week visiting her family bach of 50 years and was horrified by the brown cloudy lake water.

“Right now it looks like pea brown soup and it’s not safe to use. It’s just awful. You should be able to see down into the depths of the lake, that’s how the lake got its name and why fishers and holidaymakers love it so much,” says Ms Martin. 

“This lake is incredibly important for wildlife, like diving birds that need to be able to see prey in the water to feed. We’ve wrecked their only home. The councils responsible need to do better.”

The latest report from Environment Canterbury shows Lake Clearwater is polluted with nutrients from farmland runoff, and it has not met the Canterbury Land and Water Regional Plan (LWRP) standards since 2005 (see pages 117-120).

Other lakes in the area are in even worse shape, like the small and shallow Lake Denny which has hyper and super-trophic states on a regular basis and has never met LWRP standards. Lake Emma, which is popular for wildlife and fishing and surrounded by intact wetland areas, is also enriched with nutrients and has never met LWRP standards. 

Māori Lakes, the poster child for the Hakatere Conservation Park and the O Tu Wharekai restoration project, are also showing significant declines in water quality. The catchment of these small but vital wetlands has seen almost 100% intensification over a short period of time.  

“Neither district nor regional councils are doing enough to protect fresh water. There are standards in place and monitoring is occurring, but after 15 years of failing to meet their own standards the Regional Council has not taken the actions necessary to actually stop intensification and the extensive use of fertilisers.”

“They need to take action now. We could lose these incredible natural lakes and essential habitats. I worry it may already be too late,” says Ms Martin.

Strong compliance and enforcement systems, like the ones for Lake Taupō, need to be in place to protect lakes around New Zealand.