Fast Moving Spacecraft diving sideways then rising up.

On highway 5 coming back from L.A. to San Jose. My wife notice an object beside us in the sky about 500 yards from the highway . It was around 1:00am,the sky was black and out beside us was a reservoir of some kind .
At first I thought it was a remote control plane but then it was persistant and came closer getting bigger .That is when I realized that my wife was getting nervous as I was driving on the highway. We were all alone on the 5 .
I then looked really good and slowed down to about 40 mph from 85mph. The object was about the size of a car ,with lights;red,white,orange. It moved diving sideways down to the water of the reservoir fast ,very fast,then stopped and floated up slowly. It did this manuever about 6 times then came right beside the car and floated. Long enough to then get my attention really good.
That is when I observed a Metal object that I have never seen before in my life Moving in the night sky ,Diving sideways to the earth then floating up and reapeating this manuever several more time . Then in the blink of an eye disappearing in the sky.
It was not a plane or a remote control airplane. My wife was left very nervous and scared after the sighting. I admit that I was a bite nervous. After I noticed that we were the only ones on the highway .I got real nervous .
I never told anyone about this incident until know for reasons that are personal and will not be talked about. 
It is hard to describe the shape because the craft looks different from other angles. I know that it was not that big, it had no windows that I could see, It had lights on the craft.  
The ship was possitively some kind of Metal; silver in color ,with a dark black scraches.
Witness does not indicate a date for the sighting.  We have written him, requesting clarification on this issue.  PD