Below the Millpond
By Reed F. Curry
There's still a sturdy granite-block dam spanning the river where a nineteenth-century mill once stood. In deep summer, barely enough water comes over the spillway to maintain a calf-deep flow in the fast water below, but the water directly below the dam remains deceptively deep, and well oxygenated by its travel over the rough rock wall. This short, wide, pool lies in shade after seven o'clock in June, and then the fish, smallmouths and browns, start to emerge from the depths for their evening feed.
Low head dams, those with a height of less than fifteen feet and a top spillway, provide a unique environment for both warm and cold-water species of fish. Generally, there is a wide, deep, protective pool at the base of the spillway, tapering abruptly to shallow water in the tail. The fast water coming over the dam in the spring scours the tail of the pool, providing a bottom of mixed rocks and gravel, ideal for smallmouth spawning. The millpond above is rich in insect life which is often swept over the spillway and trapped in the churning water long enough to attract the attention of waiting fish. You can never be certain what species is rising for your fly, it might be a brown trout, smallmouth bass, or a visitor from the pond above, perhaps a sunfish or crappie. Generally, though, the trout or bass will control the best oxygenated sections of the pool, keeping them clear of the panfish.
At times of low water the pool can only be approached with caution. A 4wt, or less, line and a 12’ leader provide the delicacy necessary to success. My favorite spillway holds browns all year long, even when the rest of the river is too warm, but these are wary fish, unlikely to rise to a fly until shadows are on the water. This limits the fishing time to a few hours before full darkness but that doesn’t permit rushing casts. I usually work the 80’ pool from left to right, keeping casts short and crouching low below the tailout. If no hatch is in evidence, I’ll start with a #16 Grizzly Variant, on a long 5x tippet. This gives the fly a delicate laydown, that, combined with a breeze from the spillway which sends the fly skating across the surface, sometimes brings up the most reluctant feeders. This is a valid opening gambit, but with only twenty casts before I need to rest the pool, it pays to make each cast with confidence. If the variant doesn’t get a rise after four casts, I’ll switch to a terrestrial -- a grasshopper or beetle bounced off the wall of the dam -- since these are common fare and provide more protein to draw the fish to the surface.
Resting a pool is not a common practice in our fast-paced lives, but it pays to take a twenty-minute break from casting every so often. Fish don’t have a long memory and even a short hiatus from the disturbance of line and fly is enough to allow them to return to active feeding. Find a comfortable midstream rock, sit down and watch the swallows, or cast your fly to bats, the best of the evening is still before you.
All low head dams are not created equal. Vertical rock dams permit the water to spill directly into the pool below, creating a short reverse eddy as the water falling from above forces its way to the bottom drawing downstream water with it. This "roller" or "boil" is usually short and occurs only within the first ten feet of the pool. Fishermen should never venture too near this boil for fear of being drawn into the vortex and drowning. Stay back from the depths of the pool for all your fishing.
Far more hazardous are the low head dams with a sloping spillway which often have a "stilling basin" of concrete that extends some distance from the face of the dam. These are highly dangerous structures that create multiple backwash currents. According to the State of Pennsylvania. "The most dangerous hazard on a river is a low-head dam. There are more than 2,000 such dams on rivers and streams throughout Pennsylvania, and they are true "drowning machines." Water going over a dam creates a back current, or undertow, that can pull a boat into the turbulence and capsize it. This hydraulic can often trap and hold a person or a boat. Dams do not have to have a deep drop to create a dangerous backwash. During periods of high water and heavy rain, backwash current problems often become worse, extending farther downstream. A small low-head dam that may have provided a refreshing wading spot at very low water can become a monstrous death trap when the water level rises."
The Conservation Aspects of Low Head Dams
Low head dams, three to fifteen feet high, are common throughout the United States and Canada. From the arrival of the first European colonists through the late nineteenth century, the mechanical power potential of dams fueled rural economies. Some dams were built to power the early grist mills and sawmills; others are a product of the Industrial Revolution, as woolen mills and other factories tapped the free power of water. Few communities here in New Hampshire have just one low head dam. In my town the major brook, scarcely ten feet wide for most of it's five mile length, passes over three rough granite milldams, relics of the eighteenth century. The small millponds these create remain as local "swimming holes". Removal of these small dams would not restore Blood Brook to a pristine trout stream... the flow of water is regulated at the headwaters by a massive earthen dam that created a water supply reservoir for a neighboring community. Conservation and restoration issues are notoriously complex. Low head hydro dams were constructed to generate electricity for rural communities; many remain today, still pouring electricity into the regional power grid. The history of these power dams is often interesting. One, in Prince Edward Island, only generated electricity from sunset to 10 P.M. (after which all good people should be in bed) and on Monday mornings for clothes washing and Tuesday morning for ironing. Today, removal of a dam such as this might profit the fishery, allowing “salters” (sea-run brook trout) and salmon entrance to the upper spawning beds, with but little impact on the regional power supply. However, each such dam must be examined on its own merits.
Your own dam
You'll have to find your own dam, I've found mine. It isn't much, but it's close to home. There is usually a breeze from the spillway blowing cool mist over me, a kindness appreciated on a hot summer’s evening. Last night a white marabou Muddler twitched across the surface brought a 12” smallmouth charging up. It doesn’t get better than this.