So far in the Northwest, this has been a winter of extremes: a full month of ultra-low water, then weeks of near flood stage. I've been switching my tackle back and forth from light heads and short tips to massive heads and long tips, and I've burned through flies I rarely get a chance to fish.
But now, given these ocean currents and the pending storms, I'm guessing we're in for a long spell of heavy flows and murky water. These conditions can be ideal swinging conditions, though the river might not look like you remember. Here are some strategies I use to find clients fish during high water:
1) Selecting holding water: Go high, go inside. Those sections of the river that are high in the watershed tend to remain fishable long after the lower portions of the river blow out. Look for those runs or pools that you normally don't fish because they're too slow; ideally, they'll be above or below heavy water and contain some fish holding structure like boulders or ledges. Target your search on a section of the river that has a big bend; inside seams can stay fishable long after everything else has blown out.
2) Selecting flies: Go big, go black. Dark flies show up well under murky conditions, much better (on the rivers I fish anyway) than light colored flies. So I like to fish black patterns that are also rather large, upwards of five inches, during high water.
3) Effective Presentation: Go short, go tight. When most guys show up on a swollen river, they continue to target the lies that hold fish under normal conditions, that is to say those lies in mid-current. Rarely, though, will steelhead be holding in those places during high water events. Instead in these runs, they slide to the shores, where the bank itself offers a break from the current and cover from predation. As a result, I suggest my clients fish a short line in such places, often only twenty feet, and use the rod tip to steer the fly all the way to the bank. Snagging grass or willows means your fishing where the high water steelhead hold. Most folks also try to sink their flies all the way to the bottom in the middle of the run, meaning their fly will snag when it comes close to shore, where the fish often are. If I think the fish will be tight to the bank, I remove the weight from my flies to keep them fishing well all the way to the bank.
On the last high water event, I watched a chrome fish come out from under a bank and take a black Intruder in a lunging jump; it landed with a slap as loud as a beaver's tail--leaving the angler stunned. All of this happened just twenty-five feet downstream of where he was standing.
One more tip: we often like to think that water level determines when a river is "blown." However, fishable runs remain on most rivers even when a river is cranking at flood stage. The real determiner of when a river is "blown" is water clarity, not height. For me, I continue to fish a river with confidence if I can still see my feet when I wade in to my knees.