For some Washingtonians, Rock Creek Park is the place they drive through every day or where they hike on weekends. But others  have never ventured in to discover the hidden life at the heart of the city. Whether you’re new to the park or not, here are seven facts you probably didn’t know:

1. Scientists have detected six species of bat in Rock Creek Park, including the northern long-eared bat, which the U.S. Fish and Wildlife Service is considering listing as endangered.

2. The park has five playgrounds.

3. Stormwater run-off is one of the main problems confronting the park. Along some small tributaries, eco-engineers are replacing concrete pipes and culverts with cobble riffles and shallow  pools, hoping that sand and sedge plants as well as tiny sludge-eating tubifex worms and caddisflies will sift and clean the water.

4. About 700 permits are issued to picnickers each year. To reserve a shelter, go to or call 877-444-6777. A half-day costs $25.

5. About 60 permanent employees and 20 temporary employees work there.

6. Eighteen so-called “Weed Warriors” carry permits allowing them to tackle 30 of about 150 invasive plant species that have been identified in the 1,750-acre park.

7. Teddy Roosevelt used to go skinny dipping in Rock Creek.