Impact of dredging on water quality and bottom-dwelling organisms

DEFINITION: Removal by excavation or suction of sedimentary materials from the bottoms of lakes, rivers, estuaries, and coastal areas

Dredging is performed to maintain navigation systems, exploit mineral resources, or remove polluted bottom sediments. The activity of dredging disturbs bottom-dwelling organisms and has negative impacts on water quality. It also generates waste sediment, which must be used or disposed of in an environmentally responsible manner.

Natural erosion processes, sometimes enhanced or exacerbated by human activity, break down rock and soil into sediments that ultimately migrate downstream. When suspended sediments eventually sink to the bottom of a lake, river, estuary, or bay, they form deposits that can impede navigable waterways or increase the likelihood of flooding. Dredging, or removing underwater sediments with digging or suction equipment, keeps ports, harbors, and waterways open for commerce, security, flood control, and recreational purposes.

Dredging also serves as a mining method. Where suspended sediments contain ore minerals, the dense ore particles sink more readily than non-ore materials and form concentrated deposits. Diamonds, cassiterite (a major tin mineral), ilmenite (a titanium ore mineral), and gold are among the minerals mined by dredging. Other resources obtained through dredging include sand and gravel, which are used in construction. In areas where land is expensive, dredging river bottoms for these materials is an alternative to quarrying them on land. For example, dredging along the Kansas River in the Kansas City, Missouri, metropolitan area has provided a local source of sand and gravel for many years.

Another reason for dredging is to remove polluted bottom sediments from a body of water. Contaminant removal by dredging generates its own problems, as disturbing the sediments allows toxic materials that have settled out of suspension to reenter the overlying water, where they can affect aquatic life or be transported to another location. Maintenance dredging for navigation purposes is similarly problematic when it occurs in bodies of water where sewage or industrial pollutants have contaminated bottom sediments.

Large quantities of sediment are displaced during dredging operations. In the United States alone, maintenance dredging of navigable waters generates several hundred million cubic yards of sediment per year. In Southeast Asia, large dredges used to mine tin deposits handle more than 5 million cubic meters (177 million cubic feet) of sediment annually.

Dredging can mobilize existing contaminants, but it is not in itself a significant source of pollutants. However, dredging disrupts the habitats of bottom-dwelling organisms and can kill them outright. In addition, the dredging process and associated dumping of waste sediments in open waters cause turbidity (water cloudiness caused by suspended particles), which can harm or kill organisms that need clear water to survive. Oysters, for example, are detrimentally affected by turbid waters. Dredging can also affect erosion patterns, river flow, and ocean currents. In the Kansas River, dredging has removed far more sediment than can be replenished naturally. This has resulted in increased riverbank erosion, a wider and deeper river channel, a lowered water surface, a steeper bed gradient, and loss of vegetation and farmland along the river.

Clean dredged sediments can be employed for beneficial purposes, among them replenishing beaches and creating wetland habitats. They can also be dried and used in construction materials or as fill dirt. Heavily polluted waste sediment must be sent to a secure disposal facility equipped to handle the contaminants in question.

In the United States, concerns about environmental degradation and watershed management issues related to dredging led to the adoption of a national dredging policy in 1995. The National Dredging Team (NDT), a multidisciplinary group made up of representatives from several governmental agencies and cochaired by the Environmental Protection Agency and the Army Corps of Engineers, serves as a forum for implementation of the policy. The NDT works to ensure that timely dredging operations keep navigable waterways open while protecting, conserving, and restoring the coastal environment. A priority of the NDT is the beneficial use of waste sediments. Regional dredging teams and other interagency efforts also continue work aligned with NDT's goals.

Bibliography

Bray, R. N., ed. Environmental Aspects of Dredging. Taylor, 2008.

Dredged Material Management: Action Agenda for the Next Decade. US Environmental Protection Agency, 2003.

“National Dredging Team.” United States Environmental Protection Agency, 15 Nov. 2024, www.epa.gov/marine-protection-permitting/national-dredging-team. Accessed 29 Sept. 2025.

Palermo, Michael R., et al. Technical Guidelines for Environmental Dredging of Contaminated Sediments. US Army Corps of Engineers, Environmental Laboratory, 2008.

Peacock, Chris. "What Is Dredging? How Does It Affect Water Quality?" Aquaread, 17 Jan. 2024, www.aquaread.com/blog/what-is-dredging-how-does-it-affect-water-quality/. Accessed 29 Sept. 2025.

"What Is Dredging?" National Ocean Service, 16 June 2024, oceanservice.noaa.gov/facts/dredging.html. Accessed 29 Sept. 2025.