Australian divers who explored to a depth of 200 metres in one of the world's deepest flooded caves, near Nelson, have discovered three new animal species.

The seven divers carried out 74 difficult dives into the Pearse Resurgence in Kahurangi National Park, over two weeks between December 2010 and January 2011.

Their findings were only recently verified and this week revealed to the public.

The divers were on the hunt for any types of stygofauna, fauna that lives within ground water systems, and were surprised to discover three previously undiscovered species - a transparent amphipod, a worm and a small snail.

"It's definitely a positive sign for the environment," NIWA scientist Dr Graham Fenwick, who studied the species, told NZ Newswire.

"They play a vital role in helping to clean up environments and maintain water quality by feeding on any contaminants and anything else in the environment (that seeps through the ground and into the water). This discovery adds to New Zealand's biodiversity."

All three species are yet to be named.

It was tricky work for the divers trying to nab the little critters - the transparent amphipod and oligochaete worm are up to 8mm long and the minute gastropod snail is just 1.5mm.

The divers collected some using a suction tube, while small traps using shrimp as bait were laid up to 120m below water level to capture others.

Each deeper dive lasted nine to 12 hours but less than one hour could be spent cruising around as it took up to eight hours for each diver to surface after they had stopped at decompression "stations" as they ascended.

The divers - led by Richard (Harry) Harris) from South Australia - funded the expedition themselves with help from the National Geographic Society.

Also on the expedition were brothers Samuel and Joel Vermey from Queensland, Craig Challen from Western Australia, John Dalla-Zuanna from Victoria, and Grant Pearce and Ken Smith from South Australia.