Recreation and Aesthetics

Water Quality

Ambient Water Quality Criteria for Colour in British Columbia: Technical Appendix

8. Recreation and Aesthetics

8.1 Effects

Visual clarity is an important attribute of natural waters because it has a strong influence on their perceived recreational value, particularly for swimming and diving. Several studies have found that a minimum water quality of 1.1 to 1.2 m black disk sighting range (=1.4 to 1.5 m Secchi disk depth) was required before the water was considered to be suitable for bathing by 75% of the public (Smith and Davies-Colley 1992; Smith et al. 1991). These studies also showed that yellow-hued waters are poorly regarded, whilst green-yellow waters are considered marginal, and green to blue colours are preferred (Smith and Davies-Colley 1992). Green to blue waters generally have a true colour of less than or equal to 15 mg/L Pt (Wetzel 1975; McPherson and Miller 1987). Public perception of water quality based on clarity and colour are very similar for both aesthetic and bathing uses (Smith and Davies-Colley 1992).

8.2 Literature Criteria

Most criteria for the protection of recreation and aesthetics water uses for true and apparent colour are narrative statements. For example, a compilation of state and federal criteria by the US EPA indicated that ten states were using terms like "substantial visible contrast", or "substantial change in turbidity" (US EPA 1980; US EPA 1988). In Europe, for colour of bathing waters there is the standard "no abnormal change" (EEC 1976).

To protect the aesthetic quality of a water body, Australia and New Zealand specify that the natural visual clarity of water should not be reduced by more than 20%, and the natural hue of the water should not be changed by more than 10 points on the Munsell scale (Australia 1992; New Zealand 1994). The Alberta water quality guideline for most water uses is that colour should not be increased more than 30 mg/L Pt above natural value (Alberta Environmental Protection 1994). The Canadian water quality guideline for recreation and aesthetics states that a secchi disc be visible at a minimum water depth of 1.2 m (CCME 1987). No rationale is provided for the guideline beyond a general concern that "swimming areas are clear enough for users to estimate depth and to see subsurface hazards easily". The Japanese water quality guideline for aesthetic uses is 40 mg/L Pt, while the guideline for water use involving public contact is 10 mg/L Pt (Takahashi 1991).

8.3 Proposed Criteria

8.3.1 Apparent Colour

The 30-day mean Secchi disk sighting range should be greater than or equal to1.5 m. This criterion applies to freshwater, estuarine and marine aquatic systems. The 30-day mean calculation should be based on a minimum of five weekly samples taken over a period of 30 days.

8.3.2 True Colour

The 30-day mean true colour of water should be less than or equal to 15 mg/L Pt (i.e., blue to green water). This criterion applies to freshwater, estuarine and marine aquatic systems. The 30-day mean calculation should be based on a minimum of five weekly samples taken over a period of 30 days.

8.4 Rationale

The apparent colour criterion is based on the studies conducted in New Zealand on public perception of what constitutes acceptable water quality for recreational uses (Smith and Davies-Colley 1992; Smith et al. 1991). No other studies were available concerning the effects of colour to this water use. More stringent site-specific ambient criteria (i.e., Secchi disk sighting range greater than or equal to 4 m) will be required for recreational waters used for diving. Stricter criteria will ensure that potentially dangerous submerged objects are visible to divers.

Several studies have shown that yellow waters are poorly regarded and blue to green waters preferred by recreational water users (Smith and Davies-Colley 1992; Smith et al. 1991). In general, waters with a true colour of less than or equal to 15 mg/L Pt should be in the blue to green colour range (Wetzel 1975). Systems that are naturally coloured are not normally used for recreational purposes, and thus this criterion is not based on a change in background levels. The method for determining true colour is the same as that described in section 4.3.2.

The sampling design used to determine whether the colour criteria have been exceeded as a result of an anthropogenic activity needs to be flexible. Some considerations include availability of historical data and/or reference sites, nature of the anthropogenic activity (e.g., point versus diffuse sources), and various legal and economic issues. Short-term changes in true and apparent colour (e.g., <24 hours) can arise due to natural events (e.g., storms) but are unlikely to have serious impacts on primary producers. Therefore, when testing whether a particular anthropogenic activity has caused an increase in colour above the water quality criteria, five weekly samples should be taken over a 30-day period and a mean calculated (or median if the data are right skewed).


	Water Quality Ambient Water Quality Criteria for Colour in British Columbia: Technical Appendix 8. Recreation and Aesthetics 8.1 Effects Visual clarity is an important attribute of natural waters because it has a strong influence on their perceived recreational value, particularly for swimming and diving. Several studies have found that a minimum water quality of 1.1 to 1.2 m black disk sighting range (=1.4 to 1.5 m Secchi disk depth) was required before the water was considered to be suitable for bathing by 75% of the public (Smith and Davies-Colley 1992; Smith et al. 1991). These studies also showed that yellow-hued waters are poorly regarded, whilst green-yellow waters are considered marginal, and green to blue colours are preferred (Smith and Davies-Colley 1992). Green to blue waters generally have a true colour of less than or equal to 15 mg/L Pt (Wetzel 1975; McPherson and Miller 1987). Public perception of water quality based on clarity and colour are very similar for both aesthetic and bathing uses (Smith and Davies-Colley 1992). *8.2 Literature Criteria* Most criteria for the protection of recreation and aesthetics water uses for true and apparent colour are narrative statements. For example, a compilation of state and federal criteria by the US EPA indicated that ten states were using terms like "substantial visible contrast", or "substantial change in turbidity" (US EPA 1980; US EPA 1988). In Europe, for colour of bathing waters there is the standard "no abnormal change" (EEC 1976). To protect the aesthetic quality of a water body, Australia and New Zealand specify that the natural visual clarity of water should not be reduced by more than 20%, and the natural hue of the water should not be changed by more than 10 points on the Munsell scale (Australia 1992; New Zealand 1994). The Alberta water quality guideline for most water uses is that colour should not be increased more than 30 mg/L Pt above natural value (Alberta Environmental Protection 1994). The Canadian water quality guideline for recreation and aesthetics states that a secchi disc be visible at a minimum water depth of 1.2 m (CCME 1987). No rationale is provided for the guideline beyond a general concern that "swimming areas are clear enough for users to estimate depth and to see subsurface hazards easily". The Japanese water quality guideline for aesthetic uses is 40 mg/L Pt, while the guideline for water use involving public contact is 10 mg/L Pt (Takahashi 1991). *8.3 Proposed Criteria* 8.3.1 Apparent Colour The 30-day mean Secchi disk sighting range should be greater than or equal to1.5 m. This criterion applies to freshwater, estuarine and marine aquatic systems. The 30-day mean calculation should be based on a minimum of five weekly samples taken over a period of 30 days. 8.3.2 True Colour The 30-day mean true colour of water should be less than or equal to 15 mg/L Pt (i.e., blue to green water). This criterion applies to freshwater, estuarine and marine aquatic systems. The 30-day mean calculation should be based on a minimum of five weekly samples taken over a period of 30 days. *8.4 Rationale* The apparent colour criterion is based on the studies conducted in New Zealand on public perception of what constitutes acceptable water quality for recreational uses (Smith and Davies-Colley 1992; Smith et al. 1991). No other studies were available concerning the effects of colour to this water use. More stringent site-specific ambient criteria (i.e., Secchi disk sighting range greater than or equal to 4 m) will be required for recreational waters used for diving. Stricter criteria will ensure that potentially dangerous submerged objects are visible to divers. Several studies have shown that yellow waters are poorly regarded and blue to green waters preferred by recreational water users (Smith and Davies-Colley 1992; Smith et al. 1991). In general, waters with a true colour of less than or equal to 15 mg/L Pt should be in the blue to green colour range (Wetzel 1975). Systems that are naturally coloured are not normally used for recreational purposes, and thus this criterion is not based on a change in background levels. The method for determining true colour is the same as that described in section 4.3.2. The sampling design used to determine whether the colour criteria have been exceeded as a result of an anthropogenic activity needs to be flexible. Some considerations include availability of historical data and/or reference sites, nature of the anthropogenic activity (e.g., point versus diffuse sources), and various legal and economic issues. Short-term changes in true and apparent colour (e.g., <24 hours) can arise due to natural events (e.g., storms) but are unlikely to have serious impacts on primary producers. Therefore, when testing whether a particular anthropogenic activity has caused an increase in colour above the water quality criteria, five weekly samples should be taken over a 30-day period and a mean calculated (or median if the data are right skewed).