'Do nothing' about dwindling Canterbury lake level, hydrologist says

Retired hydrologist John Waugh says the “most useful thing you could do is do nothing” at Canterbury's Lake Camp.

Waugh was invited to the Ashburton Water Zone Committee on Tuesday to share his expertise on the situation at Lake Camp.

• Deep concerns for shrinking lake

He’s been going to the Ashburton Lakes since the 1960s and recalls times Lake Camp went low and other times it overflowed emphasising the lake's natural fluctuations.

“The best thing you could do is actually leave it alone and let it operate as a natural system.

“It’s been operating like that for 12,000 years.”

Lake Camp's water level has dropped considerably, sparking a community campaign to restore a diversion of the Balmacaan Stream, which had a resource consent up until 2020.

Last week the Ashburton District Council directed staff to prepare a report to understand the costs and implications of pursuing a consent to re-establish the diversion.

Waugh said the diversion will “barely balance the evaporation loss from the lake's surface”.

“Especially during periods of low flow. If you get one of these dry spells the lake is just going to go down anyway – and it’s always done that.

“There appears to be no ecological reason to divert water into Lake Camp.”

Diverting water “is not actually doing anything useful apart from making water-skiing a bit easier to carry out”.

“There is always an environmental cost to actions that take and divert natural flow.

“It may be nice to divert some water into Lake Camp but somewhere else in the system pays for it.”

Lake Camp is deep, has good water clarity, strong Macrophyte beds (submerged aquatic plants) and is paved with kākahi (freshwater mussel), he said.

“Organisms that are quite fussy about the conditions they live in.

“The fact they are there suggests that Lake Camp is relatively healthy. It’s not perfect but it is consistently better than most of the other lakes.”

It also suggests the lake has never dried up in the last 12,000 years he said.

Lake Camp has dropped 3.61m since 2021 through to August, but in the last few weeks has risen 49mm from rainfall he said.

It will likely continue to creep up in small amounts with rainfall, unless there is “a single big dollop” like in May 2021 Waugh said.

The neighbouring Lake Clearwater has a big catchment area and flowing streams going into it but  Lake Camp has no natural tributaries, making its water levels more vulnerable to changes in weather patterns he said.

By Jonathan Leask, Local democracy reporter

LDR is local body journalism co-funded by RNZ and NZ On Air.