Large triangle shaped ship approx 40 to 50 ft tip to tip hovering over bridge

On our way over to my house, my brother, myself, and a friend of ours were crossing over a bridge when i noticed this large triangle shape hovering over the bridge. It was approx 40 to 50 ft from tip to tip. Their were three lights, one on each corner, which did not blink. We stopped the car on the bridge and watched. Looking up at the ship we could see what looked like a massave amount of hydrolics and smaller shapes covering the underside. It hovered for about 10 to 15 minutes above us. I estimate its altitude at 40 feet above us. I didn't believe what I was seeing until it started to move away (silently) and I could see it's reflection in the river below. We watched as it desended to about 30 feet above the river, at this height it was about eye level with us. It then followed the river heading west. The one thing I couldn't understand was that it did not seem to have any height. It was thin. I have no idea as to the size of the ship other than the dimensions I have already given. I realize this report is already almost 20 yrs old but it helps to tell people, especially people who believe you.