The Delta variant of Covid-19 is now the most common strain in the country, according to Public Health Wales.
There are now 315 cases of the variant in Cymru, which is an increase of 131 cases since the last update on June 10.
The case numbers are expected to rise further over the coming weeks.
Localised community transmission of the variant is evident— with the majority of new cases not being connected to international travel.
The majority of the Delta cases have been focused around clusters of cases in Conwy and Sir Ddinbych in the north.
Dr Giri Shankar, Incident Director for the Coronavirus response at Public Health Wales, said: “This is a significant development, but one we have predicted, as we know the Delta variant is easier to catch than the previously dominant Alpha variant. It is thought that increased mixing is contributing to transmission and we are concerned at this rise in cases."