from a sideview looked like very large dark rectangles moving above the water very quickly,,no sound ...

In the winter... I just purchased a used Tahiti tri-hull and drove from my hometown in Oakdale Ca to Lake Don Pedro with friends..  virtually no one else on the Lake,,,.we ran out of gas (the gauge was not functioning and stuck on full)....two of us stayed with the boat and myself and a friend started walking around the lake back to Flemming Meadows....we stopped to rest and 2 very large rectangular objects equal distant apart went flying above the water,,,across the area of the dam..,behind an Island and disappeared...definitely not a boat or  aircraft,,,very very fast!,,no sound,,,and stayed and equal distance apart...I describe them as the size of  boxcars,,,,,I had never seen what I would consider to be a UFO prior nor since,,,
Witness indicates that date is approximate.  PD