Several streams critical to the biodiversity of the Rotorua area are being stabilised through dual council commitment.

The Bay of Plenty Regional Council has been firming stream banks with rock armouring, re-establishing trout habitats and has planted over 700 native plants to help regenerate the Ngongotaha Stream after flash flooding caused significant erosion in April.

It is working alongside the Rotorua Lakes Council in key areas.

Repairs at five separate erosion sites on the Ngongotahā Stream before were expected to be completed before Christmas, the council's area engineer Kerry Smith said.

Smith said his team had also just finished repairs to the Utuhina and Puarenga streambanks with the placement of 700 tonnes of rock armouring (assembling broken stones).

About 600 tonnes of rocks should help regenerate the Ngongotahā Stream too, he said.

Rock armouring will strengthen and stabilise the local stream banks prone to fragility because of the light pumice and soft soils. When the sites have settled, grass and native plants will be added.

The regional council has also been working alongside the Rotorua Lakes Council on stream erosion repairs.

This includes identifying opportunities to repair significant erosion sites on stream banks which have an impact on properties, reserves, walk and cycle ways.

Smith said that other work underway by regional council included gathering cross-section survey data on the Ngongotahā Stream which began in the last few weeks.

Rock armouring by the Bay of Plenty Regional Council.

The survey is expected to be completed in January.

'The cross-sectional survey involves measuring stream capacity and recording width, depth and bank height at 70 sites along the stream,” Smith said.

Smith said locals using the Ngongotahā Stream over summer should avoid tripping on survey pegs, leaving on place any they may find.

The Rotorua Lakes Council's sports, recreation and environment manager Rob Pitkethley working with the regional council had been positive.