DETROIT—While spoons and spawn work well with spinning and bait-casting rods for steelhead in the St. Mary’s River, a more effective technique in the shallow riffles usually is a two-fly nymph rig under a small float.

This rig puts the flies at the right depth and is still relatively easy to cast 20-30 feet with an 8-weight rod.

Guide John Giuliani likes to use leaders about 10 feet long.

The first part is a foot-long piece of 40-pound monofilament with a loop on the end, to which he loops a 5-foot section of 10-pound mono.

The float is slipped into the 10- pound mono.

Giuliani likes to use small ovals about the size of an acorn, pegged into place and easily slid up and down the line to suit the water depth, but any of the so-called strike indicators will work.

To the end of the 10-pound monofilament he ties a 2-foot piece of fluorocarbon (eight or six pound test, depending on water clarity) at the end of which is the first fly, usually a No. 10 or 12 caddis pupa.

The second fly is tied directly to the bend of the first hook on another 18 inches of fluorocarbon. Giuliani starts with a single egg pattern in 10 or 12 for the bottom fly, but he’ll switch to a second nymph or a bigger fly like a wooly bugger if the egg pattern isn’t productive.

Getting the flies to pass the fish at the right depth is crucial, accomplished by adding one to three small split shots above the knot that attaches the 10-pound line to the tippet.

Ideally, the flies will sweep past the steelhead at eye level. If there’s too little weight the flies will pass over the fish and usually will be ignored. If there’s too much weight they’ll hang up on the rocky bottom.

The casting technique is simple— drop the float on the water 10 feet above the slick or riffle where the fish are holding, throw a big upstream bend in the fly line and lift the rod hard if the float goes under.

Hopefully, there will be a hard pull in return.