Work's underway to try and boost the population of native shellfish as their numbers plummet

Research shows at Lake Rototoa, near Auckland, the kakahi, or native freshwater mussel population, has dropped by 85-percent.

The species is vital for filtering algae and bacteria from the lake's waters, supporting the ecosystem.

Auckland Council Senior Biosecurity Advisor, Belinda Studholme , says recent trials of protective enclosures for kakahi beds have produced breeding, a first in four years.

She says the next step is replicate this on a larger scale for wider impact.