The Friends of Castle Cove group said the crew for the E4 show “discarded” plastic confetti and table ornaments at the beach near Weymouth on Saturday.
Volunteers cleared some of the waste but said some was washed into the sea before they could get to it.
Programme maker Renegade Pictures said it “unreservedly apologised”.
The show, broadcast on E4, follows partners taking control of planning their weddings without any input from the brides.
An episode was filmed at the secluded sandy beach near Weymouth on Saturday.
Steve Elsworth, of Friends of Castle Cove, said he had received an apology from the producer but said he told him members were “incensed… at the casual way that you polluted the sea with plastic”.
“Our followers were too late to stop them leaching into the sea,” he posted in a statement on Facebook.
“The pristine nature of the cove is one of the reasons why it is so treasured by our community.”
Renegade Pictures series producer Bob Gowing said the company would be offering to assist with any further clear-up or compensate for the damage caused.
“We apologise unreservedly for the upset we have caused to the local community, who had been so welcoming and helpful during our filming period,” he said.
“Renegade Pictures are committed to sustainable filming practices including reducing plastics, however, we will be thoroughly reviewing our procedures to make sure that in future, we have a clear plan in place to avoid unexpected environmental damage, as that seems to have caught us out this time.”
Access to the privately-owned beach was blocked off for five years after a landslip but a new set of steps was opened earlier this year following a successful fundraising campaign mounted by the Friends of Castle Cove.