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".

The 27-year-old flyweight became the fastest Welsh boxer to win a British title with a points victory over Louis Norman at Ice Arena Wales in Cardiff.
It was the Barry fighter's fifth outing as a professional, having made his debut in October 2015.
"I want to be world champion, but there is no rush," said Selby, brother of IBF featherweight champion Lee Selby.
"Get some more 12 rounds in, maybe defend it, go for the European [title].
"There is no point chucking me into the deep end straight away because I have only had one 12-round fight."
No Welsh fighter has claimed a Lonsdale belt in fewer bouts and in less time since turning professional.
Norman, 32, had lost only one of his previous 13 contests.
Norman weighed in 0.9lbs over the eight-stone limit, but made the weight with seconds to spare after stripping completely naked.
The fight was on the undercard of Lee Haskins' successful IBF world bantamweight title defence against Ivan Morales and Selby says it was a great occasion at Wales' new boxing venue.
"It's the belt I've always wanted since I was a little kid," he said.
"Winning in my home town, in front of all my friends and family, you couldn't ask for better. It's a dream.
"You could just hear everyone screaming... I'd enjoy fighting here again."
A volunteer diving group is to trawl the Pembrokeshire coast to clear up lost or discarded lobster pots which endanger marine life.
[NEXT_CONCEPT]
Boxer Andrew Selby is in no hurry to win a world title after securing the British flyweight crown on Saturday.