Techniques - Nymphing and Current Speed

Current Speed

When rigging up and selecting flies for nymphing a river you need to consider the type of bug you are targeting and the current speed of the water. Current speed is one of the most important things to keep in mind when selecting and fishing a nymph pattern
Most nymphs generally live under rocks near oxygenated water – water with a steady current. When water conditions are high with faster flows, nymphs get pulled from the rocks in which they live. When the nymphs are ready to hatch they swim to the surface or crawl out onto land. In either cases, the “heavy flows and water”, means faster current, which will sweep the nymphs downstream.
Think of the nymphs being drug down stream as silt. The heavier the silt, the faster it settles in the water. As the current speed slows, the nymphs will either swim to the surface and hatch out or fall back to the bottom and crawl under a rock and find a new home..
With this in mind, it makes sense that the bigger nymphs will hatch in heavier water and the smaller nymphs will hatch in slower water.
On the Lower Yuba River there are many different nymphs, primarily, caddis, stoneflies and mayflies.

Stonefly Nymphs

The stonefly nymphs will crawl from the river bottom, out of the water, and hatch out on the rocks, so when fishing a stonefly nymph you should concentrate your fishing close to bottom and the water’s edge where the nymphs are more likely to be. This will require more weight, more than you think, hint. Stonefly nymphs come in a variety of sizes, some of them rather large, so think of them as silt – bigger nymphs in heavier water.

Mayfly Nymphs

The mayfly nymph swims to the surface to emerge. These nymphs range from tiny to small and are more vulnerable to heavy current. The slower the river current, the easier the nymph can swim to the surface to emerge. The faster the current and the deeper the water, the farther downstream the nymphs will emerge on the surface from their lie on the bottom. With this in mind, fish the heavy water with your nymph close to the bottom. if you are seeing the beginnings of a hatch you may find that as the current slows, fish the nymph higher up in the water column, lower your indicator or maybe change to a dry dropper or a emerger, dropper combination.
Caddis Nymphs
The caddis nymphs tend to live in the riffles and the tactics are somewhat a combination of the above two methods. As the caddis tumble downstream they will fall towards the bottom so fish your imitations in the flow at the current seams and deep. If there is no indication of a caddis hatch keep your presentations deep. If you see a caddis hatch progressing you can then change up your rigg to fish the upper levels of the water column with a dry dropper, emerger with dropper or rigg up to swing soft hackles.
Remember, current speed and the type of bug you're targeting can dictate your tactics and rigging methods. Don't get caught rigging up one way and not changing up as conditions dictate. A rigg chance can turn the fishing back on.