Worthing's award-winning beach has lost the right to fly the coveted Seaside Award flag for the first time in eight years.
The resort, which was a winner last year, has failed this year because it did not meet the strict water quality criteria.
The awards, which allow resorts to fly blue and yellow flags, are organised by environment charity Encams, behind the Keep Britain Tidy campaign.
Encams yesterday announced 12 beaches in East and West Sussex were among this year's successful entries, judged on criteria including cleanliness, access and first aid provision.
But Worthing was named as one of 14 from last year's 317 winners to miss out.
However, it was good news for Eastbourne, where the pier to Wish Tower section of beach is one of a few to win a flag every year since the awards were launched in 1992.
Bexhill, Birling Gap, Bognor east of the pier, Camber, Eastbourne Tower to Holywell, Hastings at Pelham, Littlehampton, Pevensey Bay, Seaford, West Wittering and Winchelsea are also among a record 332 British beaches which will get to fly the flag throughout the summer.
Angela Howard, regional director of Encams, said: "Encams demands all Seaside Award winners reach high standards, showing the beach is well maintained with a good range of facilities."
The water has to be up to the European Union minimum legal standards for cleanliness.
This is the first year since 1995 that Worthing has failed to get the award. Although it failed on water quality, the beach received "excellent" ratings in 15 categories - just one short of the number needed to get a blue flag.
Kim Long, Worthing Borough Council's economic development officer for tourism, said she was disappointed but not worried about the quality of Worthing's bathing water.
She added: "We will do everything we can to get the award next year."
Southern Water and the Environment Agency are investigating Worthing's failure to win the Seaside Award.
A spokeswoman for Southern Water said: "The council is investigating whether there were illegal connections into our system. It's possible someone has connected a wastewater pipe into our surface water.
"Obviously we are not the only people who have sewage systems and surface water systems."
An Eastbourne Borough Council spokesman said: "Eastbourne is thrilled to be celebrating a double win of the national Seaside Award for the quality of its beaches.
"We are also pleased this year to receive a new Rural Award for the quieter Holywell beach."
Seaside Awards are only given to authorities which apply. Brighton and Hove City Council has never taken part.
A council spokesman said: "We weren't aware of the scheme. We do, however, believe that our seafront is excellent.
"Water off beaches in Brighton and Hove has met quality standards laid down by the European Bathing Water Directive since 1994."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article