FYI: If you DON'T know the area..........
Here's the "bridge" at Canyon Lake:

View to the south east
Cove is to the left (south west)
There is no spillway under or near the bridge, and the lake area SW of the bridge ends in a cove where many people set camp up for the night. Many people sleep out on their boats. Something dumped over the bridge would make noise. There are trails leading to the cove before you even reach the bridge that would access the shore within yards.
The runoff into Weeke's Wash comes from the lower areas SW of Canyon lake, NOT the lake itself. Canyon Lake feeds Saguaro Lake through the Salt River, as the Salt River feeds into Canyon Lake from Apache and Roosevelt Lakes.
The remains would have to travel over 15 miles of jagged volcanic rock, trees, stumps, etc. etc., with not a whole lot of loss of altitude.
This is the bridge, about 1 mile north of the remains on Apache Trail, that Weeke's Wash runs under towards the recovery site.

View to North

View to South
To find more, go to Google maps and enter "Apache Trail & Lost Dutchman's Blvd, Apache Junction, AZ" and "Canyon Lake, Maricopa, AZ"