If You're Headed Out to Mountain Creek Lake, a Heads-Up: "Suspicious Device" Under Bridge
The dive team grabbed the bag, threw it in a boat, looked inside at the device and realized it was indeed something potentially dangerous. At which point it called in Dallas Fire-Rescue's bomb squad, which is headed out thataways now. Till they can figure out what the what it is, the bridge has been shut down both ways. Mountain Creek Parkway has also been shut down from Keist to Grady Niblo.
Update at 4:54 p.m.: DPD just sent out an e-mail asking news helicopters to evacuate the area pronto: "They are going to detonate the device." Turns out, it was in fact a grenade bomb: "a grenade, wires and three plastic bottles." The pin had been pulled, but the pressure plate remained intact.