In Washington County, you're not allowed to use a pavilion that you haven't reserved, even if it's sitting empty, according to Jaime Dick, parks coordinator for the Washington County Parks Department.
The rules are less strict at public parks in Berkeley County, W.Va., according to Steve Catlett, director of the Martinsburg-Berkeley County Parks & Recreation Board.
Picnickers are welcome to use empty pavilions as long as they clear out if someone with a reservation shows up, Catlett said. Anyone who reserves a pavilion gets written confirmation to take along to the park to prove their claim.
The Chambersburg Recreation Department has a similar policy for the pavilions at Memorial Park in Chambersburg, Pa., according to assistant superintendent Julie Unruh.
Washington County's no-squatters rule also holds true for county ballfields, Dick said.
Many people don't know that they can't just go out and play on a county ballfield that's not being used, he said.
The ballfields have to be reserved, Dick said.
When a field has been prepared for a league that has paid a fee, you don't want a family or group of friends coming in first for a pickup game and messing up the field, he said.
Pick-up games are allowed at empty ballfields at Memorial Park in Chambersburg as long as players relinquish the field if it turns out someone has reserved it, Unruh said.
Area park systems also differ on dog policies - some welcome them and others ban them - so it's smart to check first.
Safety concerns and courtesy for other pool-goers are at the root of public pool rules, written and unwritten.
No running around the pool is one of the biggies, both for that person's safety and the safety of others, Tri-State park officials agree.
Horseplay in and around the pool, pool toys, glass containers and alcohol are other universal no-nos, they say.
Regardless of whether it's stated in the rules, young children should be within reach of a parent or other adult supervising them. Older children should be monitored for safety and misbehavior.
Before dropping off a child at a public pool, make sure the child meets age requirements for being there without an adult. Different pools have different rules about children and supervision, with some allowing older children to watch their younger siblings and others requiring an adult.
For hygiene reasons, swimmers should shower with warm water and soap before going into the pool and should never urinate in the pool.
Children who aren't potty trained should be dressed in plastic pants or leak-proof diapers designed for swimming.
The golden rule for any public recreation facility is to clean up after yourself and leave the area you use as you found it.
-- Pool and park do's and don'ts