"Horrendous" parking problems at Virginia Water lake in Surrey over the bank holiday weekend led to police issuing more than 100 fines.
Officers said "inconsiderate motorists abandoning their cars all down the A30" seriously affected people trying to use the road at Windsor Great Park.
Sgt Iain Weaving said vehicles were left in cycle lanes and on the verges.
He said other members of the public had been "very supportive" of the police because their journeys were hindered."
Sgt Weaving added: "It appears that motorists either did not want to pay to park their car safely inside the park or were reluctant to find alternative parking."
He warned anyone intending to use the park in the warmer weather to use the proper car parking facilities.