March/April Stream Update


As the streams of south-central Pennsylvania transition from winter to spring, we are experiencing more optimal water temperatures and the first spring fly hatches as aquatic nymphs become mature, larger and more active in preparation for hatching.

Midges provide a mainstay for surface activity throughout the month. Look for rhythmic feeding activity in slower stretches of stream exhibiting a silty bottom substrate. Size 24 – 26 adult and pupal imitations fished on a light 6 or 7X tippet are effective. Downstream pile casts are often more productive for presentations to these wary fish, providing increased casting accuracy to fish in compressed feeding lanes with less likelihood of spooking them.

Blue-Winged Olives (Baetis) emerge from late March to mid April. Surface feeding to these flies (duns) usually takes place in medium to slow stretches from midday through the afternoon, especially on overcast humid days. Dry flies in sizes 16 - 20 which match the silhouette and color of the naturals are effective. Prior to surface activity, systematically fishing a small #16-18 brown-olive nymph in medium to fast riffles yields larger fish on average. From mid to late afternoon, the spinner of this species takes on a rusty brown color and crawls under water to lay eggs.

Early Brown Stonefly (Strophopteryx fasciata) activity takes place from mid March through April. The nymphs emerge by swimming to streamside structure, crawling out of the water, hatching and molting. Egg laying activity is important to the dry fly fisher and typically occurs in late afternoon. Adults flutter on the surface of the water while mating and ovipositing eggs into the water. Adults are a size 14-16 with a reddish brown to gray body. A palmer hackled imitation skittered across the surface mimics the egg laying activity, and although unorthodox is very effective!


Strong hatches of Blue Quills (P. adoptiva) occur from mid to late April during the late morning to early afternoon hours. Egg laying and spinner activity usually takes place from around 2 to 6 pm. A size 16-18 Adams dry fly is a viable imitation of the dun, while spinners take on a brown color after molting.

Strong hatches of tan, black and olive caddis will occur from mid to late April with predictable subsurface feeding on the pre-hatching pupae. This is a particularly important hatch on our freestone mountain streams, providing the angler with the first “match the hatch” opportunity of the season on these streams. At least two of these caddis species come back to the water to drink during the molting process, providing exciting dry fly action throughout the day.


During non-hatch periods, small nymphs in sizes 16-18 fished close to the bottom on a dead drift represent the overall food source which trout are conditioned to at this time of year. Aquatic worms, sucker spawn and sculpin imitations are effective when the water is rising or off-colored.

Trout are cold-blooded animals and their metabolism and therefore their need for food is based on water temperature. Where trout hold and how and when they feed – on a seasonal, day-to-day and hourly basis – can be plotted by water temperature. When an increase in water temperature is combined with increased food activity and availability and a growing forage base, fly anglers will experience more memorable days on the water as the spring trout season commences.

Recommended fly patterns for March/April:

Blue-Winged Olive Thorax #16-20
Adams Parachute #16-18
Early Brown Stonefly #14-16
Griffith’s Gnat #20-26
Olive Flashback Hare’s Ear Nymph #16-18
Olive Copper John Nymph #14-16
Tom’s Sculpin #8
San Juan Worm #12-16
Rusty Spinner #16-20
Tan Caddis #14-16
Black Caddis #20

Fish and stream photos courtesy of client and professional photographer Mark Sargent, after a wonderful day of guided fly fishing.