Quote Originally Posted by brokentrail
This is an interesting and informative thread. I have to say I was a little overwhelmed last week when I first hit Lake Union. All the boat slips in such deep water definitely threw me for a loop. As a matter of fact, I went in search of a weedline and some structure that I actually knew how to fish as I didn't really know what to do around a boat slip in 30 foot of water. Maybe now I have a bit of a better idea. :-)

(sorry for the long post )

That all rings 100% true. One quick tip that will help when eliminating water is that the bass in there won't ever go deeper than 15'-18' deep. The salt water that get's into the lake from the Ballard Locks tends to settle on the bottom 5'-15' of lake. Crappie and perch can live in brackish water but those smallmouths do not like it so they have to stay pretty shallow. On L. Washington there can be times when you're only gonna catch bass if you're fishing in 40'+ of water. That'll never happen in Union because of the saltwater in there. It can get so bad during the middle of the summer that the bass will move out of there completely. Then you can head over to the Mountlake Cut and nail 3-4lbers back to back in the early morning because most of the bigger bass from Union will stack up there until Fall.

This link gives a little more info about the lake and it's salt content: http://dnr.metrokc.gov/wlr/Waterres/lakes/LakeUnion.htm

The sediments of Lake Union are very soft, relatively deep, and contain a large amount of organic material. Milfoil and other macrophytes, washed into the lake from the rest of the watershed, contributes a large amount of the organic material. As microorganisms in the sediment break down this material they consume much of the oxygen in the lower part of the lake. By the end of the summer, concentrations of dissolved oxygen in the hypolimnion of Lake Union are near zero.

The intrusion of salt water forms a saline wedge that flows up the bottom of the ship Canal and the lake. Because salt water is more dense than freshwater, the salt water flows along the bottom and is not easily mixed with the overlying, less dense freshwater. The result is less mixing and a much stronger and longer lasting stratification of the lake. The saline bottom water becomes devoid of oxygen early in the summer as the oxygen is used by bacteria consuming the organic sediment.

Lake Union now flushes (complete exchange of water) about once a week at high water flows, although there is a significant amount of short circuiting of flow, where the inflowing water does not completely flush the lake before flowing out of the lake, but flows mostly in the north part of the lake from the Montlake Cut to the Ship Canal. At the same time, the opening of the Ship Canal allows periodic influx of salt water from Puget Sound. The actual balance between the salt water intrusion and the flushing rate at a given time varies with the amount of their respective volumes. During the rainy season and spring thaw, runoff from the Cascade foothills is high and the lake is flushed. As the flow drops off in the summer and boat passage through the lock increases, the intrusion of saltwater through the locks increases.