This generally occurs in mid March through Mid April but can be even later if the spring is cold. This is the best time of year to catch real quality smallmouth bass. As the water temps begin to warm into the fifties big female smallmouths will move out of their inaccessible winter haunts onto sloping points out of the current or with the least amount of current available at the time. No current is best but often the river is flowing hard this time of year so it's easiest to look for eddies where the current is flowing upstream as these currents are always milder than downstream currents. Any hard point extending into the current is a likely spot to try. The fish may move up and down these points on a daily basis so don't be discouraged if a spot does not produce it's likely that it will at some point during the season. As the fish move to the shallow end of the point they'll be more aggressive and likely closer to the current break. The best way to target them at this time is with a quickly moving fly that is large and fished at their level. They are feeding primary on crayfish but they are often sluggish and need some enticement to get them to react to a fly. Expect this type of activity a little later in the day after the water has warmed a few degrees. If the fish are not up shallow your best bet is to back off the point a little and concentrate the deeper slower side of the point with patterns that you crawl along the bottom S...l...o..w...l...y.
As the spring progresses the fish will move further back into the cove created by the point. The larger and more isolated the cove is the more fish it will hold but they will also be spread out more. If you catch one fish concentrate on areas that are at the same depth and distance from the main river. these fish are "staging" for the spawn and are often very aggressive in spite of the still cool water covering lots of water with large flashy or even noisy flies will cause a reaction bite. This is the time of year you'll see tournaments won with fish that average 4-5 lbs. Covering as much water as you can is the name of the game. Even covering the same area every few hours can produce as more and more fish move into spawning areas.
ok this is longer than I expected I'll cover the spawn, post spawn, summer and fall later on...
Smallmouth in the river will begin spawning in late April and last through early June depending on the weather. The warmer and more stable the conditions are the earlier and shorter the spawning season. During this time the bass will not feed however will aggressively attempt to rid it's nest of intruders it deems as a threat. Covering shallow backwaters quickly is the key to catching lots of fish. If the water is clear enough and wind calm enough sight fishing is an option. In these conditions you'll want to use a fly that you can easily see. Cast it beyond the nest and slowly work the fly into the middle of the nest and leave it there. The longer you leave it there the more agitated the fish will become. Sooner or later they will strike... If both the male and the female are present the male will likely take the fly and remove it from the nest, do not set the hook on him, wait till he spits it out and throw it back on the nest until the larger female eats it.
If all you are catching is small males it's most likely due to the fact that the females have laid their eggs and moved out to the first drop off, even if it's a small one. Female smallmouth usually go into a non-biting funk immediately following the spawn but knowing that they are on the first depth change puts you where they are. Try natural looking flies fished slowly.
After the spawn and even the males have left the nest smallmouth can become difficult to find and quality fish even more difficult. but after 2 or three weeks you'll begin to find them actively feeding on current breaks quite the same places one might look for feeding trout. The points of islands, points in rip-rap banks. Any structure that juts out into the current making a seam is likely to hold some fish. Offshore rock piles and submerged Islands are other key areas. Having good maps and electronics on your boat can be of great assistance in finding these spots. During this summer season as with the rest of the year the forage base is mostly crayfish and scuplins. it is very common to catch fish with crawdad antenna or a sculpin tail sticking out of their throats. However they will also start targeting bait fish. This is when the top water bite starts to happen. During this season it's just about any technique will work it will be a matter of trial and error to see what the fish want on any particular day. Some days it will be slow and on the bottom, other days you won't be able to strip your fly in fast enough. Look for wind blown shallow banks with millfoil for super aggressive fish. on Sunny calm days expect to fish deeper.
By about Mid august the American Shad fry that were spawned in the spring will hatch and begin their downstream migration This is the time of year that every bass fly angler should be looking forward to as the smallmouth gorge on them. large top water flies fished quickly will often produce fish all day long even on the hottest of days also large baitfish patterns produce when the top water bite is off. Often times you'll see several fish following your hooked fish to the boat, this is a great time to fish with a buddy and have him pay close attention while you are landing a fish so you can double up by catching the chasers... This season of fishing will last until mid September and progress downstream as the shad smolts migrate.
Sorry about joining this discussion late but in another life I fished bass (both largemouth and smallmouth) quite a bit. On the wet side of the mountians the smallmouth game is a lake game with the best lakes being fairly large. I see folks have talked about some of the smaller lakes - that is a largemouth game -another discussion.
Smallmouth in our lakes will be mostly a deeper water game (depedning on the season/water temperature) you will be doing your fishing in 5 to 30 feet of water. So you need to have lines that gve you the flexibility to fish those depths - your 8 wieght would be fine. While smallmouth are generally thought of as being a fish feeding along 10 to 25 deep gravel flats and underwater points they can be attractive to structure as well. Isloated boulders, logs, tree tops and docks all can hold respectbale #s of fish. \
As Rob stated the pre-sapwn is an excellent time for large fish as they moving into the shallower waters. As the smaller lakes and ponds move into that the 50- degree range it is time to think about moving to the large lakes for smallies as those lakes will be a few degrees cooler. They wil spawn during the first stable weather once the water temp reachs the mid to upper 50s - here in W. Washington that will typically be during May. Expect the spawn period to last 3 to 4 weeks (longer or shorter depending on the weather patterns). The males will be constructing their beds in 5 to 15 feet of water on gravel flats and they like having some structure (rock, log, dock poiling, etc) on one side. The males will guard the bed site until they eggs hatch. Once the fry leave the beds the adults move back towards deeper water. There can be short lull post spawn in the fishing but expect consistent fishing the rest of the summer once you have the fish patterned
While the smallmouth game in our lakes is one of mostly large nymphs, streamers, etc do not over look surface poppers and large dries; especially just before and during the spawn as well as low light periods the rest of the summer. I tie most of my smallie flies on hooks ranging in size of 4s to 1/0. One of my best flies is a Woolly bugger tied on a 1/0 low water Atlantic salmon hook using a full marabou feather for the tail in a variety of colors combos. You will also want scuplin and baitfish streamers in the 2 to 5 inch range, large nymphs (dargon and damsel flies), leeches, etc. Those flies can be fished on 6 and 8# tippets with leader lengths being a little less than the rod length.
Since if you are targeting smallies on larger lakes some sort of boat is a must. A bow mounted electric is a huge asset though lots of fish can be caught out of boats using oars, anchors, etc. A wind sock can be handy for slowing down wind drifts across likely flats and edges. From Seattle north besides Sammamish and Washington other lakes that produce excellent smallmouth fishing include Stevens, Goodwin and Whatcom. 1 to 3# fish should be the norm though decent numbers of 4 and 5# fish are found in all those lakes with that odd stud of 6 or pounds.
A depth finder is a huge help in zeroing in on some of that key structure though keeping an eye on the other bass fisheries will help locate that water. Before I got my first finder I found some of my best hot spots by watch the coots and noting where they were bring up weeds from off shore locations - found several 15 to 20 foot humps and flats in unexpected locations that way (which by the way still produce fish).
While you will not likely see many fly anglers on those lakes there is some excellent fishing to be had for the "feather tosser".
With a sunken forest on the west side, rocky structure and docks throughout, Lake Sammamish is an excellent choice for a lake that is close to home.
I haven't fished Stan Coffin before, but other good East side choices are the Columbia and Snake rivers, and Moses, Banks and Palmer (but don't tell anyone else) lake's.