Pāpāwai-Mangarara stream flows alongside Pāpāwai Rd in Greytown to join the Ruamahanga River.
The Pāpāwai Marae-based group expects restorative plantings to reach target numbers in the next three years.
Gibson said it was mainly humans impacting the health of the water and levels of biodiversity of freshwater species. Sediment and the lack of trees were largely to blame.
"This would have originally been part of a wetland complex that surrounded Wairarapa moana, and those wetlands were drained for farmland and a lot of the trees were cut down," she said.
The result is a lot of sediment in rivers and streams.
"That would have been a big problem as sediment fills up all the gaps in the bottom of those streams, it can take away all those spaces for the food to grow, but also the places for things to live and hide," Gibson said.
"That's had a really big negative impact.
"Also, the stream flows through quite an urban environment. Because of that, it can have impacts from stormwater, from roads ... farm runoff as well can be an issue."
The group set freshwater traps looking for eels and fish species, and collected water samples to look at the different species in the stream.
"If we found all of the different kinds of whitebait species, that would be incredible," Gibson said. "So the banded, the giant, the short jaw kōkopu... kōaro are another fish that likes really clean, healthy, quite bouldery rivers and streams, and then inanga as well.
"This is a place where I would expect to probably find inanga, it's low-lying. If there is access to the ocean for these fish to get back up here, then that would be really amazing."
"Kākahi or freshwater mussels are another species that you see in some of the streams around the area, so the presence of those tells us that some fish would be present too, and they're really good at helping to clean up the water themselves as well."
Over a few hours the team found one injured long-fin eel and a broad mix of medium to low-sensitivity species like water boatmen, sandfly, midge larvae, amphipods, worms, damselfly larvae, and a very small number of the more sensitive mayflies.
Gibson said the findings told experts a lot about water quality.
"Our findings on this day tell us there are some water quality and habitat issues which we then investigated with further tests," Gibson said.
In order to restore biodiversity, volunteers will need to continue with riparian plantings, increase shade cover over the stream and stabilise areas around the river-bed to reduce erosion.
• For more information about how to get involved, visit www.waip2k.org.nz.
