An underwater pest which can have a major impact on the local wildlife has been discovered in the waters off Cardiff Bay.
The mussels filter vital nutrients from the water
The Zebra mussel, which is a not native to the waters, is thought to have been introduced by a visiting boat.
Each mussel can filter between one and two litres of water a day, taking away algae and other organisms which birds and fish thrive on.
It is thought to be the first time the creature has been found in Wales.
Previously they have been found in the River Thames and Lea, and Lake Barden, Kent. Other sightings have been made in Yorkshire and Cambridgeshire.
As well as causing ecological harm, the mussel, which reproduces rapidly, can damage the engines of boats.
Growth in large masses can lead to engine blockages or over-heating.
The Cardiff Harbour Authority (CHA) is warning boat owners to carry out routine maintenance of their vessels to limit this build-up and prevent such problems occurring.
David Hall, environment officer at CHA, said .Zebra mussels "have the potential to cause huge ecological change in our freshwaters".
Research was being conducted to assess the implications on the ecology of the area.
Native to Caspian and Black sea basins
They are transported via the bottom of boats
They attach themselves to solid objects underwater
They reproduce rapidly
One mussel can filter up to two litres of water a day
David Lowe, operational manager the CHA added: "The impacts in other parts of the UK and Ireland emphasise the importance of preventing Zebra mussel spread to other fresh water areas in Wales."
"Our advice and guidance on Zebra mussels outlines the way forward and we are asking all water users to follow this guidance as a priority."
It's the first time the species has been discovered in Wales
Dr Tristan Hattan-Ellis, senior freshwater ecologist for the Countryside Council for Wales, said that the containment of the Zebra mussel was vital.
"I am pleased to see that CHA are taking such a responsible approach to this problem species.
"Literature already available provides an excellent step towards help prevent the spread of Zebra mussels into other fresh water areas, where they could do major damage to native mussel populations and perhaps to the whole ecology of the site."