(a) Draining of wetlands lowers average water table elevations. It may increase downstream peak flows and, if normal flow channels are blocked, decrease water storage capacity and downstream base flows. Secondary impacts may occur, such as a successional change in wetland vegetative covertype toward drier types, increased water temperatures, and changes in fish and wildlife use. Complete draining can eliminate wetland vegetation or wetlands themselves.

(b) Dredging, excavating, or channelizing wetlands, or removing soil, mud, sand, shells, or other aggregate from wetlands may increase water depth and remove wetland plant species, altering the basic substrate characteristics. Wetlands may be eliminated by creating water levels too deep for wetland vegetation to survive. Fish and wildlife feeding or reproductive use may be altered. Water storage capacity may be increased while changes in covertype variability, turbidity, sediment deposition and substrate erosion may result.

(c) Filling, dumping, or construction of roads may decrease wetland area, hence decreasing the multiple benefits derived from wetlands. Impacts may extend beyond the boundaries of the filled area especially if surface or subsurface water movement is affected. For example, loss of storage capacity may result in increased sedimentation of adjacent waters. Ancillary use of the filled area could lead to runoff or leaching of noxious materials or chemicals. Extraneous material incompatible with the wetland (such as certain metals or waste oil and other chemicals) may adversely impact water quality and fish and wildlife use. Such activities may degrade the aesthetic character of the wetland. Ultimately, filling may eliminate a wetland entirely.

(d) Creation of impervious surfaces in wetlands, irrespective of other associated developmental activities, may increase surface runoff and thereby may increase turbidity, sedimentation and water flow through wetlands. Increased water flow through wetlands may increase erosion, interfere with natural biological and chemical processes, change covertype patterns, and alter temperatures. Decreases in the functional capacity of wetlands may result as may also introduction of incompatible materials or chemicals (such as trash or gasoline) from the impervious surface over wide areas of the wetland.

(e) Erecting structures in wetlands, irrespective of other associated developmental activities, may shade and thus alter wetland vegetation, obstruct or interfere with surface or subsurface water flow, and interfere with fish and wildlife use.

(f) Placing obstructions or driving piles in wetlands may interfere with surface or subsurface water flow, or increase water levels, thus affecting wetland water supply, flooding potential and vegetative patterns. The level of impact is related to the amount and location of obstruction. The placing of piles for support of other structures may be a reasonable alternative to placement of fill when water storage capacity or hydrologic absorption values are the primary benefits derived from the wetland, especially when such placement of piles will not create a hazardous obstruction to flowing water containing ice or other water-borne material.

(g) Introducing wastewater treatment effluent or installing septic tanks or sewer outfalls in wetlands or adjacent areas may contaminate ground or surface water with undesirable nutrients or organisms. Excessive nutrient loads may alter the vegetative composition or fish and wildlife use, and/or affect the suitability of water for human use. Organisms introduced with wastewater effluent may create a general health hazard. Effluent may increase successional rates through the introduction of excessive levels of nutrients or by warming ambient water temperatures. Abnormal levels of water may be created in wetlands. These impacts may interfere with fish and wildlife as well as human use of water resources.

(h) Construction of dams, dikes, and other impoundments and control structures in wetlands or on water bodies running through them usually increases water levels or restricts water flow, altering or eliminating wetland vegetation, and may destroy whole wetlands.

(i) Other regulated activities may introduce or increase toxins, noise and other forms of pollution, remove or reduce vegetation or expose soil to erosion. Such activities include, for example, the operation of all-terrain vehicles and airboats, construction of utilities in existing or new corridors, either overhead or underground, disposal of chemicals, introduction or discharge of pollutants, application of pesticides and other chemicals, disposal of solid wastes, clearcutting or other timber harvesting practices, and construction or removal of groins, bulkheads, berms or levies.