Walnut

Meadville, PA – The Pennsylvania Fish and Boat Commission announces that geotechnical drilling operations will be taking place in the Walnut Creek channel area starting Monday, July 9, 2012. Operations are expected to be completed by Tuesday, July 10, 2012. The marina and boat ramp will be open during drilling. Boaters should proceed with caution when transiting the channel.

It is just a means of evaluating the composition of the streambed and underlying geologic formations.  They will collect samples of the subsurface rock/soil and perform testing on them to determine their geotechnical properties such as density, cohesion, friction angle, permeability, ect. which can then be used to determine the stability of the area.  
 
I am not exactly sure what the specific intent of the drilling at Walnut is though.  Usually this type of testing is performed prior to construction of some type of structure, or for oil and gas exploration. 

Lol keep your balls down in the channel slick

Offshore drilling about 50 yards out from the mouth.  Building a pipeline from 16 mile to supply fracking fluid.
 
Regardless of what happens, when people complain about there not being any steelhead at Walnut in late-August, clearly it's because they are all falling into the hole.