“Silt happens!” That simple riff off a common bumper sticker is a quote from Gary Esslinger, manager of the Elephant Butte Irrigation District in southern New Mexico (Weiser 2011). His sentiment arose from desert country but might have been uttered by Exelon Power about its Conowingo hydropower project on the Susquehanna River or the owners of the recently removed Elwha River dams on Washington’s Olympic Peninsula. Or perhaps owners of some of the other power, water retention, or flood control structures that dot our landscape. The list of interests expands when those fine-grained sediments carry a heavy burden of contaminants, even mineral-grade levels worthy of a Superfund site. So here’s some dirt on the complex issue of accumulating sediments and what they mean to aquatic systems, with implications to science, management, policy, engineering, and every other field. These issues are ubiquitous because all waterways carry sediments. Where flow is interrupted, sediments drop out of solution and accumulate. If the interruption is a dam, most sediments are trapped immediately upstream of the blockage where they settle to the reservoir bottom. More sediment means less volume remaining for water, which could translate into less electrical power, water storage, aquatic habitat, recreational opportunity, etc. The silver lining is that those very same sediments also sequester significant loads of phosphorus and some nitrogen that otherwise would flush into downstream waters. Those artificial aids to restoration are appreciated until the stilled waters reach a sort of dynamic equilibrium where the reservoir is near capacity, the accumulated sediments must be removed, and potentially nasty mixes of agricultural and industrial chemicals are freed from the watery depths. This scenario is likely unfolding at some scale in every jurisdiction on every continent. The waterways that deliver sediments and chemicals remain the primary source of most pollutants, but the dams and accumulating sediments are dangerous contributors with costly ramifications. Instead of a natural flow of sediment-laden waters to nourish downstream habitats, a dammed waterway offers pulses of sediments and pollutants. As reservoirs fill, water flow slows and sediments accumulate, so the dams slowly lose their ability to generate power or store water. Those pulses then become a larger concern because they can scour the accumulated sediments and release more material, thereby opening some capacity for the cycle to happen again. Though those ecological shifts unfold in the main channel, a fine rain of sediments and chemicals falls out of suspension onto the floodplain, often increasing plant and animal production along the fringes of the larger reservoir system. Isn’t it often the way—some of what looks good always complicates what we conceive as bad! Those complex causes, effects, benefits, and costs will eventually lead river managers, dam owners, and society to discuss water and sediment budgets for the entire watershed. Inevitably, sediment removal emerges as a primary issue. If contaminants are involved, the discussion may also involve a responsible party with legal liabilities, and disposal options will narrow. That complex dance has started for the dams on the Susquehanna River and countless other facilities. The Conowingo Dam and the three other facilities on the lower Susquehanna River (York Haven, Safe Harbor, and Holtwood) offer a current glimpse at these challenges. The Susquehanna River flow and sediment load are major drivers of Chesapeake Bay ecology, including fish and their habitats. The river and the dam/reservoir/sediment are major sources of phosphorus (which tends to bind to sediments) and silt but less significant for nitrogen. A recent report by the U.S. Army Corps of Engineers (2014) concluded that the three dams upstream from Conowingo have essentially reached their limit to trap sediment. Despite that lost capacity and the reality that major weather events dispense phosphorus-laden sediments into the water column, the report concluded that the sediment and pollutant issue relates more to the river than the dam and reservoir. It is essential to discuss these issues at the watershed scale and not with respect to a single dam or reservoir. Those discussions would not be complete without dam removal on the agenda as the shifting national energy business has implications for hydropower facilities. It’s complicated. So how does this affect fish, and what should we do to address sediment and pollutant problems at the watershed level and associated with dams and reservoirs? First, we should encourage engineering solutions evident in dam designs dating back to the 14th century, adopted by the Chinese for their Three Gorges Dam but rarely part of American designs (Weiser 2011), namely, to include a gate at the base of the dam that will enable operators to flush accumulating sediments from the reservoir. Second, we need to improve sediment controls to keep soils on the land, not in waterways. Third, we need to include all parties, including agriculture, mining, transportation, power, fishing, and probably more; they all are involved as sources or part of the solution. The relative importance of these issues wavers depending on the water body, but generally a broader discussion will yield greater prospects for success. REFERENCES U.S. Army Corps of Engineers. 2014. Lower Susquehanna River Watershed Assessment, Maryland and Pennsylvania—Phase One. Draft report released October 10, 2014. Available: mddnr.chesapeakebay. net/lsrwa/docs/report/LSRWADraftMain20141010. pdf. (April 2015). Weiser, M. 2011. Sedimentation is a building problem in the West’s reservoirs. High Country News. Available: www.hcn.org/issues/ 43.6/muddy-waters-silt-and-the-slow-demise-of-glencanyon- dam/sedimentation-a-building-problem-in-the-westsreservoirs. (April 2015).