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Water Quality

Understanding Non-Point Source Pollution in BC

Introduction > Impacts on Communities > Causes of NPS > References and Links


Until recently, British Columbia's environmental agencies, like in most other jurisdictions, have focused primarily on controlling point sources of water pollution, but we are now beginning to understand the extent of NPS water pollution and the risk of not controlling it. Many costs and problems are associated with NPS pollution, including:

  • degraded drinking water and potential human risks;
  • damage to aquatic ecosystems, including fish, other aquatic organisms, and their habitat;
  • economic losses to commercial and recreational fishing and shellfish harvesting and impacts on traditional First Nations food harvesting areas;
  • diminished water-based recreation and tourism opportunities;
  • reduced aesthetic of lakes, streams and coastal areas;
  • costs of remediation (e.g. payments for monitoring, clean-ups and pollution reduction); and
  • reduced real estate values.

Non-point source pollutants in aquatic ecosystems can be grouped into five main categories:

These microorganisms-bacteria, viruses, and protozoa-can cause waterborne illnesses. While most pathogens come from human sewage (primarily leaking or aging sewage collection systems, onsite sewage systems, stormwater runoff, and combined sewer overflows), manure from livestock and wild animal droppings are also common sources.

Oxygen Depleting Substances
When organic wastes (e.g., manure, sewage, pulp and paper mill effluent) decay in water, bacteria oxidize the waste, using up oxygen dissolved in the water. If the oxygen is consumed beyond a safe threshold, fish are stressed and will die when lethal levels are reached. Anaerobic decomposition (without oxygen) produces gases, such as hydrogen sulphide, that are lethal to many organisms.

Organic wastes and fertilizers can introduce plant-feeding nutrients, such as nitrogen and phosphorus, into runoff. When polluted runoff enters a waterbody, nutrients can cause algal blooms and dense weed growth that disrupt the balance of aquatic ecosystems and interfere with recreation such as swimming and boating. When an algal bloom occurs, oxygen in the water is depleted, which can cause odour and taste problems as well as kill fish and other organisms. Certain kinds of algae may be toxic to people and livestock.


Suspended soil particles make water turbid and unpleasant to drink, and can reduce the effectiveness of drinking water treatment. Sediments also reduce light available to algae and aquatic plants, kill or injure fish by damaging their gills, cover spawning gravel and smother fish eggs, and reduce the quality of recreational activities such as swimming and boating.

Substances such as ammonia, nitrate, metals,
pesticides and a variety of organic toxins can poison humans, livestock, wildlife, and aquatic organisms. Some toxins cause cancer.

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Impacts on Communities

Across British Columbia, NPS water pollutants have produced a range of impacts. In the enclosed marine waters of the Capital Regional District (CRD), NPS water pollution has adversely affected recreational opportunities, degraded aesthetic values, and reduced the abundance and diversity of marine life. Victoria and Esquimalt harbours remain closed to commercial crab harvesting due to dioxin/furan contamination. Beach closures have been common throughout the CRD, primarily due to fecal matter discharged into stormwater systems. Although recent identification and elimination of sources of pathogens in storm drains that discharge near beaches has allowed beaches to reopen, several dozen storm drains remain a significant concern. In Saanich Inlet, most embayed areas are closed to shellfish harvesting due to fecal contamination associated with agricultural runoff, onsite sewage systems, and stormwater runoff. High levels of heavy metals have been measured in sediments near stormwater outfalls. These contaminants can cause sublethal toxicity to bottom-dwelling organisms.

In areas of the Lower Fraser Valley, east from Vancouver, the most significant potential for NPS water pollution is the agriculture industry. The Abbotsford-Sumas aquifer is contaminated with nitrate leached from manure and other fertilizers applied to crops and fallow fields. Nitrate contamination is also evident in other aquifers, including Hopington and Brookswood, due to agricultural activities and onsite sewage disposal.

Streams in the eastern Fraser Valley and in less urbanized areas of Langley and Surrey exhibit depressed oxygen levels caused by agricultural runoff. Low oxygen levels have contributed to coho salmon kills in the Nicomekl, Serpentine, and Little Campbell Rivers near Boundary Bay in the 1980's. The same conditions exist in Matsqui Slough.

In the more urbanized areas of the Lower Mainland, the negative impacts of stormwater runoff, combined sewer overflows, and occasional toxic spills have been significant. Fish kills have occurred. Nutrients and fecal contamination have reduced aesthetic values and recreational use of urban lakes. Stormwaters and combined sewer overflows contribute a significant contaminant load to Burrard Inlet, where toxic metals and organic chemicals in the sediments are potentially toxic to bottom-dwelling organisms.

Advanced sewage treatment to control point-source phosphorus loading to the Okanagan Lakes over the past 25 years has led to significant improvements in water quality in most lakes. However, phosphorus inputs from non-point sources in this area remain a concern, and account for over 90% of total phosphorus loadings in the Okanagan Basin.

In the Armstrong, Osoyoos, and Grand Forks areas, ground water has been contaminated with nitrates from chemical fertilizers leaching from orchards and other crops. Corrective action should reduce the problem, but unless other NPS pollution from agriculture, forestry and stormwater are also controlled, deteriorating ground water quality from increasing nitrate levels could continue.

In the cattle ranching areas of the Northern and Southern Interior, water pollution from agriculture is widespread. Phosphorus loadings in runoff from cattle over-wintering areas have contributed to the eutrophication of Williams Lake in the Cariboo, with blooms of blue-green algae and critical oxygen depletion in lake bottom waters. Agricultural runoff has also affected the Thompson River and its tributaries-the Bonaparte, Nicola, and Salmon rivers. Where cattle have direct access to streams, bank erosion leads to vegetation loss, bank destabilization, and damaging sedimentation. Cattle manure can contaminate drinking water and harm fish by depleting dissolved oxygen.

In coastal areas, localized discharges from boats and marinas, storm drains, onsite sewage systems, and agricultural runoff affect enclosed, poorly-flushed bays, forcing shellfish harvesting closures to prevent health risks.

In other areas of British Columbia, NPS pollution tends to be localized rather than widespread, generally associated with land development and population growth. Land development not only increases NPS pollution directly through erosion and sedimentation from land clearing and excavation, but also increases the opportunities for NPS pollution from other sources.

The cumulative effects of non-point source water pollutants, along with regulated point sources, may exceed the carrying capacity of surface and ground waters. Understanding the connection between land use, the degree of development, and water quality is important. This allows us to target sensitive areas and apply preventative solutions such as changing public behavior, applying alternate business practices or investing in innovative technologies.

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Potential Causes of Non-Point Source Water Pollution in British Columbia

The more contaminants in water, the greater the risk to humans, fish, and animals. Even small amounts of contaminants in small amounts of runoff result in cumulative effects over an entire watershed and, building up over time, can have a significant impact. Locating the sources of pollution and removing contaminants before they reach the water provides the best assurance of clean water in the future.

The main potential causes of non-point source water pollution in British Columbia are:

  1. Land Development: has its greatest effect in the major urban regions — the Lower Mainland, east coast of Vancouver Island, and the Okanagan Valley.

  2. Agriculture: can affect water quality in the Lower Fraser Valley, Cariboo, Thompson, and Okanagan basins, and the east coast of Vancouver Island.

  3. Stormwater Runoff: stormwater runoff often contaminates receiving waters in all urban areas of the province, but is of greatest concern in the Greater Vancouver and Capital Regional Districts.

  4. Onsite Sewage Systems: poorly maintained and poorly located on-site systems primarily affect populated inland lakes, enclosed marine bays, and vulnerable aquifers.

  5. Forestry: can affect fish, fish habitat and drinking water throughout the province when it causes an increase in sedimentation.

  6. Atmospheric Deposition: includes dustfall, acidic rainfall, and air emissions. Water quality effects are primarily felt down-wind from urban areas, but long-range transport of persistent organic pollutants can occur.

  7. Boating and Marine Activities: primarily affects waters around major commercial ports, boat yards, and poorly-flushed marine and freshwater anchorages.

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References and Links

Tackling Non-Point Source Water Pollution in British Columbia: An Action Plan. 1999. Ministry of Environment, Lands and Parks (now called Ministry of Water, Land and Air Protection).

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