That will lead to a further 120,000 riparian natives planted by August next year.
Project manager Lloyd McCall said he was delighted to see the first phase completed.
Listen to Jamie Mackay interview Lloyd McCall on The Country below:
"The project has exceeded its milestones and has managed this while still being under budget," McCall said.
"The success of the project was assured with strong support from local farmers on 104 farms. They have effectively underwritten the project by funding any costs beyond the agreed project contribution."
He said 99 per cent of the farmers involved were members of the award-winning PWCG - a farmer-led catchment water quality improvement body.
"Having farmers already actively taking steps to protect the environment was instrumental in securing the funding.
"Over a long weekend the group managed to get farmer contracts and commitments securing posts, wire, plants, planters and management to apply for significant project-ready funding."
Over time, the project would lead to significant improvements in water quality and biodiversity in the Pomahaka catchment, McCall said.
"It's exciting with the whole community watching as the plants are starting to grow out of their protectors. In five to 10 years the plantings will be very obvious, changing the landscape forever," McCall said.
"This has been a positive project at a time when the uncertainty of environmental regulation is at the forefront of farmers' minds."
To mark the completion of the first phase, the PWCG will plant a commemorative tree at the Leithen picnic ground, on September 29.
