Guidelines for Canadian Recreational Water Quality

4. Nuisance Organisms

Maximum Limits

The bathing area should be as free as possible from nuisance organisms that could affect swimmers. Nuisance is defined as something that can cause harm or is annoying, unpleasant, or obnoxious (Webster's Third New International Dictionary 1986).

It is impossible to have natural areas "free" from nuisance organisms, so no limits can be quantified. Only the possible hazards caused by such organisms and the environmental situations that could promote their presence are discussed.

Recreational areas should not be developed if there is an excessive growth of aquatic plants where entanglement could occur, thus causing a hazard to water-related recreational activities, unless control measures are taken to remove the plants from areas used for swimming.

Criteria

Description

Two principal types of biological factors influence the recreational value of surface waters: those that endanger the health or physical comfort of people and animals, and those that render water aesthetically objectionable or unusable as a result of excessive nutrient enrichment or the presence of unsightly substances. The former include vector and nuisance organisms; the latter include aquatic growth of microscopic and macroscopic plants.

Vector organisms

Massive emergences of non-biting midges, phantom midges, caddisflies, mayflies, etc. cause serious nuisances in shoreline communities and impede recreational pursuits (National Academy of Sciences 1973). In addition to the physical annoyance of their presence, biting insects such as mosquitoes and black-flies can inflict serious irritation from their biting attacks.

Human respiratory allergic reactions such as hay fever have been reported to be due to inhalation of caddisflies, mayflies, and midges, or their parts, when large insect swarms are present (Henson 1966).

Abrupt changes in water quality, especially if accompanied by organic loading, may precipitate high midge production. A sudden decline in oxygen supply in organically enriched bodies of water can disrupt established faunal communities and favour the less sensitive species of midge larvae and other tolerant organisms that can withstand low dissolved oxygen. Part of this change is caused by the increase in food from organic waste. Upon emergence as adults, these midges can cause a nuisance with their dense swarms.

In the marine situation, nuisance or hazardous conditions can exist at bathing beaches because of the presence of organisms such as jellyfish and some species of sea urchins.

Aquatic vascular plants and algae

Aquatic vascular plants (macrophytes) affect water quality, other aquatic organisms, and the uses that are made of the water. It is difficult to estimate the magnitude of the adverse effects of aquatic macrophytes in terms of loss of recreational opportunities or the degree of interference with recreational pursuits. For example, extensive growths of aquatic macrophytes interfere with boating of all kinds, but the extent of interference depends, among other things, on the growth form of the plants, their density, the fraction of the water body affected, and the purposes, attitudes, and tolerance of the boaters.

Dense growths of aquatic macrophytes are generally objectionable to the swimmer, diver, water-skier, and scuba enthusiast. Plants obstruct the view of the bottom and underwater hazards, and swimmers can become entangled in the fronds. Water-skiers' preparations in shallow water are hampered by dense growths of plants, and fear of falling into such growths while skiing detracts from enjoyment of the sport.

Recreational activities such as boating and fishing are less appealing and may even be almost impossible if aquatic plants are very dense. Rafts of free-floating plants or attached plants that have been dislodged from the substrate often drift onto beaches or into swimming areas. Drying and decaying aquatic plants often produce objectionable odours and provide breeding areas for a variety of insects.

Increased plant growth can be caused by the presence of excess nutrients, for example, from various agricultural practices and private waste inputs that increase the amount of phosphorus and nitrogen. The results of this increase in nutrients is called cultural eutrophication. The natural aging (eutrophication) of bodies of water occurs much more slowly and does not change on a time scale to be of significant interest in the context of this document. Increased silt loads, changes in shorelines, and land use all contribute to alterations in aquatic habitats.

Some odours from lake water originate from natural decomposition of algae and other aquatic plant materials. These kinds of odours are typically vegetable or "earthy" in nature; however, decomposing masses of the filamentous alga Cladophora in Lake Erie and Lake Ontario have been described as "pigpen" (Neil 1975).

Several species of algae produce very different, sometimes offensive odours while actively growing in lake water. Odours described as fishy, grassy, aromatic, or musty have been attributed to several species of diatoms, blue-green algae, and Chrysophyceae (Palmer 1962; Taft 1965). Nicholls et al. (1980) reported serious odour production by the prymnesiophyte Chrysochromulina breviturrita in recreational lakes in Ontario and New Hampshire. The odour produced by this species, described by cottagers as "rotten-cabbage" or "garbage-dump," seems to be restricted to slightly acidic lakes. Chara, a rooted macroscopic alga often mistaken for an aquatic vascular plant, has a very strong, objectionable odour. It is commonly found growing in extensive mats on lake bottoms (Warrington 1989).

Odours from lake water can be measured by the Threshold Odour Test (American Public Health Association 1989). The Threshold Odour Number (TON) is the ratio by which the sample must be diluted with odour-free water so that the odour is just detectable by a test panel of several people. Many natural surface waters not influenced by odour-producing algae have a TON of 5, whereas others with excessive algal growth may have a TON value exceeding 200.

Summary

1. Some biota that could be a nuisance to bathers if present in large numbers - e.g., leeches, mussels, biting insects, floating or rooted aquatic plants, phytoplankton, periphyton, and growths such as sewage fungus - should be absent from areas intended for development as bathing beaches.
2. The presence of large numbers of midges and aquatic worms, which can tolerate polluted, especially organically enriched, conditions (e.g., as caused by sewage), would indicate that the water quality was probably not good enough for recreational use.