A natural form of algae is being mistaken for sewage by concerned holidaymakers, a conservation body reports.
Natural Resources Wales says it has received reports from people concerned about sewage or slurry on the beach or in the water in places like Aberystwyth, West Angle and Pendine.
These have been investigated and found to be caused by nothing more than tiny, naturally occurring algae, called phytoplankton, that thrive in warm summer weather.
To find out more about the water quality in any of Wales’s beaches visit the Natural Resources Wales website.
Welsh beaches have been ranked among the best in the UK and across the world with 34 achieving Blue Flag status and 31 obtaining Green Coast Awards.
Pembrokeshire is home to some of the best beaches, winning 10 Blue Flags, followed by Gwynedd with eight and Anglesey with six.
The beaches were judged on criteria including cleanliness, water quality and safety.
Natural Resources Minister Alun Davies says:
"The awards demonstrate the high standard of Welsh bathing water quality and reflect the diversity of our beautiful coastline, which is enjoyed by our communities and the millions of visitors to Welsh beaches each year.
"These awards also recognise the hard work of everyone involved in achieving and maintaining these high standards."
RNLI lifeguards return to their posts around Wales this Easter weekend and have reminded beach-goers to be aware of the dangers.
From 10am the charity's lifeguards will be present at Aberavon, Neath Port Talbot, Whitmore Bay in Barry Island and Tenby South beach to offer advice and assistance to beach-goers.
All three beaches kept the lifeguards extremely busy in 2013.
Whitmore Bay was the busiest Welsh RNLI lifeguarded beach for the second year running as the lifeguards responded to 221 incidents and assisted 236 people.
"RNLI lifeguards are trained to respond to a range of incidents both on the beach and in the water," said Stuart Thompson, South Wales RNLI Lifeguard Manager.
"We work with the Ambulance Service as First Responders to deal with minor and major first aid incidents, rescue people from rip currents as well as assisting other emergency services to help search for missing children.
"It was great to see thousands of people enjoy the hot weather on Welsh beaches last summer and hopefully we'll see more of the sun again this year.
"When enjoying the coast we advise people to try and visit a lifeguarded beach and to always swim or bodyboard between the red and yellow flags - this is the area that's patrolled by the lifeguards.
"If you get into trouble raise your hand and shout for help; or if you see someone else in danger please don't try and attempt the rescue yourself - tell a lifeguard or call 999 and ask for the Coastguard."