The Tidbinbilla Nature Reserve has been closed because so many people have ignored advice meant to stop the spread of the coronavirus.
The ACT government said hundreds of people had crowded the beauty spot over the weekend.
The repeated advice has been to stay away from other people.
Gatherings have been forbidden because the more contact people have with each other, the higher the likelihood that the virus spreads far and fast - overwhelming hospitals so that they can't treat people who need treatment in order to survive.
The decision to close Tidbinbilla was "disappointing", according to ACT Environment Minister Mick Gentleman.
"This weekend over 500 people visited the reserve and were confined to a reduced area as a result of January's bushfires," Mr Gentleman said.
"We have closed the park for the safety of the community as well as our Parks and Conservation personnel."
It's not clear why people crowded there. In Canberra itself, the usual places of social gathering were relatively deserted. Perhaps people thought Tidbinbilla would be deserted, too.
The ACT government along with the NSW government, has been ratcheting up instructions to isolate and the penalties for not doing so as the public fails to do enough.
The government said more closures would happen if the rules weren't obeyed, and everyone should respect the closures.
"This means not congregating in groups larger than two, keeping 1.5 metres from others, avoiding peak usage periods and practicing good hand hygiene," Mr Gentleman said.
"Other parks and reserves across the ACT will remain open aside from Namadgi National Park, which remains closed for safety reasons following the Orroral Valley bushfire.
"Rangers will be monitoring to ensure people are using the spaces that remain open in accordance with government directions.
"If people continue to ignore the rules, we may need to close more parks and reserves."
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