November of 1991, a fierce storm over Seattle combined with a maintenance problem on the bridge deck of the old I-90 bridge segment from Seattle to Mercer Island to flood the flotation pontoons of the bridge and send it unexpectedly to the bottom.
Much of the bridge was salvaged, or dragged to deep water, but several sections of bridge decking still remain, just off shore, under the modern eastbound lanes of I90.
Today, we sent a team of 5 divers into the fresh water of Lake Washington to discover what remains of the sunken bridge.
Delaina, Rich C., Mikel & Steve M, and myself splashed at around 10:30. We made a brief surface swim from the boat landing at Day Street Park to the first set of bridge supports. Keeping our dive flag prominently displayed, we carefully swam out to the third set of stanchions, watching for boat traffic. This area is the pass through zone for traffic on the Seattle side of Lake Washington, and in the afternoon and evening it's as busy as the roads. In the morning we only saw one boat, who stayed well clear of our group.
Reaching the third set of supports, we descended on the southernmost support. Because of the amount of metal in the bridge and the wreckage, compasses don't register true, and navigation has to be by dead reckoning. Luckily, it was a sunny day, algea bloom was minimal, and we had 10 foot vis all the way to the bottom at 30ffw.
We landed on a debris field, but it was not clear if the garbage was from the wreckage or just from stuff tossed over the side of the road. We got the team oriented, and made a slow swim north to the other support, where we went over a man made "wall", and dropped another 10 feet; hitting the thermocline right at 30 ffw. The temperature dropped 10 degrees instantly, from the mid sixties to the mid fifties without warning!
On the bottom we spotted a line, which our pre-dive research indicated would lead directly to the bridge deck. We followed the line west towards shore for about 20 feet, and then turned around and backtracked. Another 20 feet past our descent point, the water ahead grew dark, and suddenly we could see the edge of the bridge decking!
We gently ascended to about 25 ffw, and glided over the deck. This section was made of metal grid, not asphault. It is now covered with some kind of lake slime, but it is still in good repair. We saw no holes. There is some debris scattered around the area, especially on the northern and southern sides of the decking. We swam east, down the slope, and south, emerging into the sunlight out from the shadow of the overhead bridge. We could still see the side railing of the bridge; an eerie sight at our depth of 40ffw. The team then turned east and slowly swam down the decking. At about 55ffw, in the pitch dark, without reaching the end of the bridge, we decided to turn the dive and return to the exit point.
Using my light, I could see down through the metal gridwork to the hollow spaces inside the decking. There are holes for access to this area at the shallow east-facing end, and I assume potentially elsewhere. This could make for a challening wreck-penetration area for those so inclined. We saw enough rope, rebar, shattered metal, and other debris to make considering such a dive something only the experienced dive team should contemplate.
We saw several small silvery fish, but none close enough to identify. We may have spotted a bass sitting on eggs in shallower water during our exit swim. At various places in the debris field we saw crayfish hiding under cover. These 3-inch long "miniature lobsters" make good eating when prepared by a chef who knows their way around a cajun cookbook, but today we were just visiting, not harvesting.
The noise from the cars passing overhead was a low hum during the entire dive, with an occasional loud roar as a semi passed by. We could also hear power boats in the lake making passes along the modern floating bridge.
At 30 minutes, we reached the tie-off point for our dive marker, and made a staged, slow ascent to the surface in 5 foot increments of 1 minute duration. On the surface, we formed a tight group, checked for boat traffic and made a quick surface swim back to the park. On exiting the water we made the quick walk to the parking area to doff gear and compare notes. Rich took several pictures (which we'll post when we get them), but my camera battery died and I was unable to take video.
Given the unique nature of the dive, I'd rate this dive pretty highly, but because it's in the lake and not the ocean, it's pretty barren without much to see beyond the debris. That makes the experience perhaps a B- in my book: I'd go back with a first timer, but wouldn't plan a special trip without an excuse.
Happy diving!
Ryan
Dove I-90 Wreck
Thanks Ryan, That was a great report!! 
Calvin,Maverick and I also dove that site a few months ago here is the Dive site listing. Looks like you guys had some better viz than we did I think we only had 5ft at best. I also dove there once and found a 2000 yukon someone dumped there!
Calvin,Maverick and I also dove that site a few months ago here is the Dive site listing. Looks like you guys had some better viz than we did I think we only had 5ft at best. I also dove there once and found a 2000 yukon someone dumped there!Who run barter town?
