File under WTF for the DC's Department of Parks & Recreation...
A parent found a full and uncapped bottle of muriatic (hydrochloric) acid at the Petworth Spray park on Sunday. The chemical is used as a cleaning agent and likely left by a DPR employee after cleaning the water pumps, etc., for the opening weekend... a very, very absent-minded employee who needs to be retrained on proper chemical handling. (Here's some examples on how muriatic acid is used.)
Read the full article and some angry comments on Popville.com.
5/27/15 Update: I followed up with the DCPR Aquatics Director.