Yo Surf - Thanks for your sad message. Here's what I've found, talking to the VFTU members and WCO Bob Bonney:
The AQUA 12 inch main broke some before 8:00am. It is upstream near Great Valley High School, and the break was bad enough to shut down Rte 401.
AQUA reported it directly to DEP
A VFTU member saw the problem and reported it about 8:10am
Bob Bonney was on vacation and we let him know directly, so he jumped down to the creek
He and a VFTU member counted a couple hundred dead fish, but the water got too turbid to see the bottom
The USGS gave showed a very sharp spike, uncharacteristic of stormwater surges, from about 20 cfs to 40 cfs (about double). The spike down there lasted about an hour, starting about 12:30pm.
By now the rest of the stream will have cleared, and the (dead) fish count will resume tomorrow Saturday morning about 10:00am. Some of the VFTU will be there to help Bonney, and if anyone here wants to help, come join this sad effort. We'll use the Valley Creek Park on Rte 29 for parking and as the base:
361 N Morehall Rd, Malvern, PA 19355, United States, GPS: 40.0606,-75.53193