(SOUTHBOUND 99 IS OPEN AGAIN AS OF 11:40 PM)

All lanes of the southbound Alaskan Way Viaduct at Atlantic Street are closed for a collision. Use alternate routes pic.twitter.com/Fzu0tQYz3E — seattledot (@seattledot) March 24, 2015

2:39 PM: All lanes of southbound Highway 99 are blocked by an overturned semi-truck in the stadium zone. More to come.

2:55 PM: The southbound Viaduct is now closed at the north end of the Battery Street Tunnel, so if you are headed that way from north of downtown, you’ll have to exit on Denny Way. Otherwise, to head south from downtown, you’ll need to take I-5 or surface streets such as 1st or 4th. We’ll keep updating this since we’re heading into the pm commute.

3:14 PM: This is affecting buses too:

Transit Alert – The SB Alaskan Way Viaduct and the stop on WB Columbia St are closed; use the stop on SB 3 Av north of Cherry St. — King County Metro (@kcmetrobus) March 24, 2015

3:22 PM: For those stuck on the Viaduct when this happened, here’s what’s being done:

SPD turning traffic stuck on SB SR 99/viaduct around and directing drivers off at Columbia & Elliott. pic.twitter.com/bkfg0xdC4d — WSDOT Traffic (@wsdot_traffic) March 24, 2015

We have another view of that courtesy of Chi Krneta:

3:43 PM: Still closed. And southbound I-5, we’re told, has a stall on the south side of downtown. Another alternative for getting back to West Seattle: The Water Taxi. Its afternoon schedule is just now starting up:

@westseattleblog water taxi has lots of room for first sailing of the afternoon — axleyjc (@axleyjc) March 24, 2015

Here’s the schedule. Meantime:

Here's another look at the overturned semi blocking all lanes of SB SR 99 at Atlantic. **Avoid SB 99 in Seattle** pic.twitter.com/34ydE2x3cF — WSDOT Traffic (@wsdot_traffic) March 24, 2015

And a view texted to us:

We’re still trying to find out if there’s any ETA for this being cleared. For now, just assume it’ll be hours, and plot your homeward alternative (or don’t leave until you hear it’s clear).

4:07 PM: SPD says a tow truck’s on the case – but that still doesn’t mean it’ll clear fast:

Tow truck working to clear SR-99 after overturned semi blocks all southbound lanes. More updates as we get them. — Seattle Police Dept. (@SeattlePD) March 24, 2015

4:19 PM: Keep in mind that there’s a domino/spillover effect in many other places. For example, if you click around on the live video cameras in the general downtown area accessible via the SDOT Travelers’ Map (lower right) – you’ll see scenes such as vehicles STILL clearing off the Viaduct backward – right now at the Columbia onramp, a bus can be seen backing toward 1st, and someone is directing traffic. Also, via Twitter, SDOT says they’re hoping to have at least one lane open within a half-hour or so.

5:40 PM: SPD now says two tow trucks are on scene.

5:45 PM: And the problem has finally been explained – “a very large load of fish” is what the semi was carrying.

6:11 PM: The Sounders FC/Club Tijuana match has been pushed back to 7:23 pm. And SPD has an update on the semitruck’s driver:

Driver of overturned fish-filled #SR99 semi taken to HMC w/non-life-threatening injuries. SPD investigating for any violations or citations — Seattle Police Dept. (@SeattlePD) March 25, 2015

6:33 PM: Latest tweet from the scene – “Responders have separated the tractor from the overturned trailer and are attempting to put the trailer back on its wheels again now.”

6:57 PM: Making progress:

UPDATE: Almost back on its wheels. They have a tractor ready to haul it away, if the effort is successful. pic.twitter.com/YwuClVTnFw — seattledot (@seattledot) March 25, 2015

7:12 PM: After 4 1/2 hours, the truck is right-side up again:

Truck is back on its wheels once more. We are getting closer to opening the roadway. pic.twitter.com/Xmnrd4Ki2O — seattledot (@seattledot) March 25, 2015

7:47 PM: Now they’re moving on to cleanup.

8:19 PM: And that’s not so easy, tweets SDOT: “Trailer contents have shifted, making it unstable to transport. They will detach trailer from truck and pull it off roadway.”

9:30 PM: Now going on 7 hours since this happened. The trailer has to be unloaded before it can be moved. We asked via Twitter, just out of curiosity, what kind of fish? Answer: Salmon.

10:05 PM: Still closed while crews work with the trailer.

10:47 PM: According to discussion just monitored via scanner, the problem is that the trailer remains unstable. It’s about a third empty now and they might try to move it again once it’s half empty. We are now in hour 9 of the total southbound 99 closure from the Battery St. Tunnel southward.

11:34 PM: They’re about to start reopening southbound 99, now that the truck and trailer have been moved successfully. They’re reopening starting at Denny, and then from Columbia.

11:40 PM: Official confirmation, 9 hours after the closure began:

Thank you all for your patience. Contractors have cleared the semi and SR-99 has reopened for traffic. — Seattle Police Dept. (@SeattlePD) March 25, 2015

That’s almost twice as long as the much-dissected 5-hour closure in June of last year following a head-on crash south of the West Seattle Bridge. Different circumstances here – no life-threatening injuries, but the wreckage posed a major challenge to clear. Some of what was promised in reports following the June incident (most notably this one) has been implemented, notably longer coverage hours in the city’s Traffic Management Center. We’ll be following up on this tomorrow, and certainly we won’t be the only ones.

11:16 AM WEDNESDAY: We did indeed inquire with SPD this morning. No direct response but they’ve published a long report on SPD Blotter which includes photos and tweets from yesterday (some of which we featured in real-time in this report) – we’re writing a separate story on this.