Cold water from 50 feet down
Blue Marsh Dam went up in 1978 as an Army Corps flood-control project, and TCO Fly Shop in Reading, the shop nearest the water, explains the part that matters to a trout: the release comes off the bottom, from depths of up to 50 feet, so the creek below it stays cold enough for trout to hold through summer. The Corps also uses the lake to push fresh water down the Schuylkill and Delaware in dry summers to hold back salinity in the estuary, which is why releases can jump without warning and why TCO says to check the flow before every trip.
The stream is float stocked with browns and rainbows every year, and the fish that hold over are the reason the Tully has a reputation: TCO puts holdover browns and rainbows at 13 to 16 inches with a few over 18, on a creek that reaches 120 feet wide in places. Two tributaries help. Plum Creek enters just below Rebers Bridge and the Cacoosing comes in beside the paper mill at Tulpehocken Road and Paper Mill Road, adding 55 to 60 degree water; in a heat wave the trout stack up below both.
Deflector one to the covered bridge
The 2026 PFBC summary defines the Delayed Harvest Artificial Lures Only section as 3.79 miles, from the first deflector below Blue Marsh Dam downstream to the T-921 covered bridge. Locals count six deflectors, built by the Tulpehocken Chapter of Trout Unlimited, and number them; TCO says the deep glide below deflector one holds good numbers of larger browns that rise to caddis, and that deflectors two through six all fish. Get there by the access road off Palisades Road to the lots at the dam, the stilling basin and the picnic area.
Downstream the landmarks come in order: the Water Works at the end of Water Road beside the Western Berks County Water Authority plant, medium-gradient riffles and long glides that get more pressure than anywhere else on the creek; then the Palisades flat, a long deep glide where the fish have all day to refuse you, and the Palisades riffle, about 200 yards of pools, ledges and pocket water with free-rising caddis eaters and Sulphur sippers at dusk in late May. Above Rebers Bridge the creek is slow riffles and pools with the best summer Trico pods on the stream, reached from the lot off Rebers Bridge Road; below the bridge it turns to riffles and pocket water cooled by Plum Creek, with parking at Paper Mill Road and Tulpehocken Road across from the mill.
TCO's flow bands on the damsite gauge
TCO keys its Tulpehocken report to USGS 01470960, Tulpehocken Creek at Blue Marsh Damsite, and publishes its own calibration: Skinny at 0 to 100 cfs, Prime at 100 to 250, Pushy at 250 to 400 and Blown above 400. The shop says the bands are its own from years on the water, not a USGS product. DIY Fly Fishing quotes 350 cfs as an ideal wading number but reads the gauge near Reading, 01471000, which sits below the Cacoosing and runs higher; the two figures are not in conflict once you know which gauge each is using.
TCO's report also carries a temperature scale, Prime from 56 to 64 degrees and Caution from 64 to 68, and draws a hard line at 68 degrees, which it calls a conservation threshold rather than an opinion: above it, give the trout a rest and fish for smallmouth and carp, which the September 2026 report was recommending during a stretch of low, clear, warm water. The USGS monthly medians at the Reading gauge since 1979 bottom out around 141 cfs in August and 157 in September, so late-summer trips are decided by temperature more than flow.
Delayed harvest: what the dates mean on the Tully
Under the 2026 delayed-harvest rules the 3.79 miles are open year-round, 24 hours a day, to artificial lures and flies only, with no natural bait, bait paste, scent or fish eggs allowed and no baitfish taken. From the day after Labor Day until June 15 the creel is zero. From June 15 through Labor Day an angler may keep three trout a day of at least 9 inches. A trout permit is required, and boaters may carry bait through without stopping to fish. Below the covered bridge, from the T-921 bridge to the mouth at the Schuylkill, the creek is on the Berks County list of Stocked Trout Waters Open to Year-Round Fishing, so the statewide season and extended-season limits apply there without the February closure.
The practical effect: the best fishing, spring hatches and fall holdovers, falls inside the no-kill months, and the harvest window opens just as TCO's temperature caution kicks in. Most regulars treat the whole creek as catch and release in summer for that reason.
Caddis first, then Sulphurs and Tricos
TCO calls caddis the staple of the Tully, with a range of species bringing even the largest browns and rainbows up from May through October, and lists Blue-Winged Olives, Sulphurs, Light Cahills, Yellow Drakes, Cream Drakes, Caenis and Tricos as the mayflies, with Sulphurs and Tricos the most consistent. DIY's dates agree: olives from March to November, Little Black and Little Brown Stoneflies in early March and April, Sulphurs from late April through June, Light Cahills in June, Tricos and terrestrials through summer and fall, midges all winter with dry-fly fishing on sunny days.
Tackle follows the bugs. TCO fishes 4 and 5 weights from 8 to 9 feet, drops to a 3 weight for Tricos, and runs leaders of 10 to 14 feet tapered to 6X, 7X and even 8X in summer, when some locals nymph on 8X. The Palisades flat is where you find out whether your drift is good enough.