The Prince of Wales has spoken out against the "global plastics plague" which is threatening the oceans and humanity.
Charles also highlighted his support for efforts to tackle the waste in oceans in a pre-recorded video message broadcast at a major Cardiff summit on the issue.
The conference is part of a number of events that marked the arrival of yachts in the Welsh capital taking part in the global challenge, the Volvo Ocean Race.
Charles said in his message: "Over the past months we have seen, at last, some decisive action taken by a range of individuals, private companies and governments in response to the growing concern about how a global plastics plague is threatening not only our seas and the wealth of biodiversity they support but also ourselves.
"Ladies and gentlemen, we simply must maintain that level of pressure if we are, to use what I understand is the name of one of your boats, going to turn the tide on plastic.
"It is not just those of us who have an affinity with the sea, but all of us who inhabit this planet who must surely share your concerns over how we have reached this crisis point."
The prince went on to say: "We simply cannot allow the current rate of degradation of our oceans to continue."
Charles highlighted how the competitors would be gathering "vital data" about the state of the waters around the continents as they raced against each other.
Buoys released by the yachts will collect information about surface temperatures, while on-board systems will provide readings on chlorophyll and carbon dioxide.