A Sunday afternoon ceremony at Rock Creek State Park near Grinnell will mark the park’s 50th year of existence, just as a group is pushing to have the lake that’s the centerpiece of the park dredged.Rock Creek Lake Alliance Bob Brierly says the project depends on state support, and while they were hoping to get things rolling in the next three years, it may take longer than that.Rock Creek State Park got its start with a half-million dollars from the state.Brierly says 12-thousand people gathered on the Rock Creek Lake dam in August of 1952 for the park’s official opening.Rock Creek State Park is about 10 minutes west of Grinnell. Sunday’s 50th anniversary celebration begins at one o’clock.