Water quality and the risk posed by contaminants and other potential stressors in water or in bottom formations needs to be understood and tracked if it is to be controlled. Contaminants in the form of pesticides, hydrocarbons and heavy metals can become available when released via disturbance and can impact water quality. Excessive sedimentation can cause direct impacts such as smothering or interfering with feeding. Elevated nutrient loads commonly enhance algae growth, gradually altering food webs or spatial distributions of wildlife, or leading to blooms that can release toxins and reduce oxygen levels.
Terrestrial runoff from rainfall and irrigation can deliver contaminants, sediments and debris through storm drains, streams and rivers to wetlands, shorelines, bays and coastal waters, impairing the quality of sanctuary resources as well as posing risks to human health. This is especially true for the nine sanctuaries with coastal boundaries. Contaminants can cause impacts that include harmful algal blooms, tissue toxicity, reproductive anomalies and elevated mortality of marine mammals. These impacts directly interfere with fishing, visitor access due to beach closures and swimming advisories, and other recreational activities.
In addition, various types of spills, likely emanating as point sources from ships or shore-side facilities, may reduce water quality in marine ecosystems. Sanctuaries have experienced hydrocarbon spills from grounded or sunken vessels often originating from locations outside sanctuary boundaries, and other potential spill sources could include damaged petroleum pipelines or platforms either inside or outside their boundaries. The effects can range from sublethal to lethal and include contamination of shallow habitats and water, physiological impacts to animals and plants and their food sources, smothering of intertidal organisms, and coating of surface dwellers like seabirds and marine mammals. Furthermore, spills sometimes require responses that include mechanical recovery, chemical dispersion, and burning, which may impact additional resources. All marine sanctuaries with either shallow habitats or shorelines in close proximity to ship traffic have reported spills as an issue. In light of these threats, marine sanctuaries are actively involved in regional spill response planning and vessel routing evaluations. Some sanctuaries also have volunteer-based beach monitoring programs to provide early warning and impact assessments.