The Knottingley and Pontefract neighbourhood policing teams used social media to remind people that they have been granted new powers by the Government to enforce social distancing rules.
"Despite the Government advice for social distancing people are still using motor vehicles to travel and do exercise and walk dogs," West Yorkshire Police's Wakefield East and South East team posted on Facebook.
They said a "large number of vehicles" were parked at the park.
"A polite reminder has been placed on the vehicles," they added.
"The initial police response will be to encourage voluntary compliance.
"This is a national public health emergency.
"People are putting their own and other people’s lives at risk, and they are contributing to placing the NHS under even more strain.
"If people do not comply with requests to leave then the Police now have new powers to issue fixed penalty notices to a value of £60. This amount doubles every time there is a breach."
The latest Government guidance says people should "stay local" - though it does not specify exactly what "local" means - and not travel unnecessarily for exercise.
"So please consider others - by adhering to Government Policy you are helping to save lives," police added.