I live next to this lake, my kids (9 & 4) and I walk around that trail frequently (2-3 times/week).
I can tell you that the odds they went swimming, or even attempted to get near the water, near where their bikes were found is remote. The fence was put between the trail and the lake there to keep people away from the lake there. The trail is at its lowest point there, uphill both directions and curving slightly, so that a biker coming up to that area is approaching fairly blind, and if was forced to swerve, the lake is mere inches from the trail there. The lake-side fence runs 50-ish feet in either direction from this lowest point. There is a gate at this point in the fence, leading to a rock jetty that gives access to the drain pipe. The highway-side fence runs along the freeway, which is under construction, reduced from divided 4-lane to 2-lane right there, very congested, very busy. A stopped vehicle there would be almost impossible, much less allowed to remain long. A couple years ago, a car slid off the road and tumbled through the ditch into the fence, about 100 ft from this narrow, double-fenced area of the trail, and it damaged the fence. It has never been repaired. The ditch is incredibly tall grass and weeds, and is difficult to traverse by foot, and there is the constant rush of traffic just a few feet above - seemingly not a place where kids would just go to explore.
I can tell you that the odds they went swimming, or even attempted to get near the water, near where their bikes were found is remote. The fence was put between the trail and the lake there to keep people away from the lake there. The trail is at its lowest point there, uphill both directions and curving slightly, so that a biker coming up to that area is approaching fairly blind, and if was forced to swerve, the lake is mere inches from the trail there. The lake-side fence runs 50-ish feet in either direction from this lowest point. There is a gate at this point in the fence, leading to a rock jetty that gives access to the drain pipe. The highway-side fence runs along the freeway, which is under construction, reduced from divided 4-lane to 2-lane right there, very congested, very busy. A stopped vehicle there would be almost impossible, much less allowed to remain long. A couple years ago, a car slid off the road and tumbled through the ditch into the fence, about 100 ft from this narrow, double-fenced area of the trail, and it damaged the fence. It has never been repaired. The ditch is incredibly tall grass and weeds, and is difficult to traverse by foot, and there is the constant rush of traffic just a few feet above - seemingly not a place where kids would just go to explore.