Neptune's Army of Rubbish Cleaners (NARC), which is celebrating its 10th year of diving for marine litter, will take to Milford Haven's waters on Tuesday.
Welfare charity World Animal Protection has funded the dive.
NARC said 20,000 lobster pots had been lost in Wales in winter storms.
The group - which has collected 70 lost pots so far this year and is working with local fishermen to locate more - said the gear could trap marine life and eventually kill them.
NARC chairman David Kennard said: "It is great to be making close links with local fishermen who are able to tell us where their gear was last sighted, giving us a chance to dive, locate and bring it back to the surface."
The group said the clearing of marine litter had a "significant impact" on the sustainability of local fisheries and biodiversity.
Christina Dixon, of World Animal Protection, said it was supporting the dive as part of the Sea Change campaign to get rid of so-called "ghost fishing gear".
A volunteer diving group is to trawl the Pembrokeshire coast to clear up lost or discarded lobster pots which endanger marine life.