Police turned away more than 1,000 cars from one beauty spot in just two days for breaching lockdown rules.
Dyfed-Powys Police said many people officers spoke to in the Brecon Beacons were from England who said they did not know about Wales’ different rules.
Supt Steve Davies said fines were issued if people had “clearly flouted the rules”.
The force said many of those stopped at the weekend claimed they thought the rules in Wales were the same as in England and came from as far afield as London and the Midlands.
Police said they were kept busy due to the volume of people trying to drive to the area around Ystradfellte, Powys, known as “waterfall country”.
The force, which covers some of Wales’ most rural areas, also said 72% of people reported for breaches of Covid-19 restrictions in Powys since 27 March had been from outside the force area.
Supt Davies said: “Our officers have worked hard to engage with the public at every opportunity throughout these unprecedented times by explaining what we are doing and why, and encouraging people to make the best choices to protect public health in Wales.
“But where people have clearly flouted the rules we have dealt with them appropriately and issued fines.”
He said officers would continue to conduct stop checks throughout Powys and across the force area this weekend.
Wales’ three national parks and all National Trust sites remain closed to the public during the lockdown, although the Brecon Beacons National Park Authority has said parts of the park will open from Monday.