Debris and tape was put across the entrance of Barlow Common to stop drivers from being able to access the car park.
Selby District Council, which manages the car park, said they were clearing the debris to allow drivers to return to the nature reserve to take exercise.
It is not known who blocked off the car park and debris was yet to be cleared on Monday afternoon.
A spokesperson for the council said: “As soon as we were alerted to the issue we took immediate action to clear the debris blocking the entrance and reopen it.
We are working to find those responsible for the unauthorised closure so we can talk to them about why they’ve done this.”
The 37 hectare reserve is normally a popular beauty spot with ramblers and nature-lovers.
Emma Ford, who lives near the reserve but drove to the car park over the weekend, said:
“I understand the reasoning behind the closure due to how busy outdoor places are but surely closing one just puts more pressure on the ones that remain open.
“It is a tricky one and the guidelines this time are so vague on travel and exercise. I personally am not going very far at all anyway due to shielding but reading the guidelines I assumed a three minute car journey would be okay.”
It comes as North Yorkshire’s police lead on coronavirus warned residents the police would take action on people leaving their homes unnecessarily.
Superintendent Mike Walker said: “It is not reasonable or essential to travel lengthy distances to take daily exercise, when it can be taken from the doorstep. We do not expect people to be travelling multiple miles in a car to take their exercise in North Yorkshire.
“I think we can get sometimes get embroiled in the detail of what we can and can’t do and lose focus on the real reason we are being asked to limit our movement and why the police are enforcing this legislation – to save lives.”