Southern Water Control Zone Statement of Water Quality Objectives
[29 July 1988]
(Format changes—E.R. 5 of 2019)
The water quality objectives set out in the first column of Schedule 1 have been established for those parts of the Southern Water Control Zone defined in Schedule 2 set opposite those water quality objectives in the second column of Schedule 1.
| A. | AESTHETIC APPEARANCE | |||
| (a)Waste discharges shall cause no objectionable odours or discolouration of the water. | Whole Zone | |||
| (b)Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substance should be absent. | Whole Zone | |||
| (c)Mineral oil should not be visible on the surface. Surfactants should not give rise to a lasting foam. | Whole Zone | |||
| (d)There should be no recognisable sewage-derived debris. | Whole Zone | |||
| (e)Floating, submerged and semi-submerged objects of a size likely to interfere with the free movement of vessels, or cause damage to vessels, should be absent. | Whole Zone | |||
| (f)Waste discharges shall not cause the water to contain substances which settle to form objectionable deposits. | Whole Zone | |||
| B. | BACTERIA | |||
| (a)The level of Escherichia coli should not exceed 610 per 100 mL, calculated as the geometric mean of all samples collected in one calendar year. | Secondary Contact Recreation Subzones and Fish Culture Subzones | |||
| (b)The level of Escherichia coli should not exceed 180 per 100 mL, calculated as the geometric mean of all samples collected from March to October inclusive in one calendar year. Samples should be taken at least 3 times in a calendar month at intervals of between 3 and 14 days. | Bathing Beach Subzones | |||
| (L.N. 453 of 1991) | ||||
| C. | DISSOLVED OXYGEN | |||
| (a)Waste discharges shall not cause the level of dissolved oxygen to fall below 4 milligrams per litre for 90% of the sampling occasions during the year; values should be calculated as the water column average (arithmetic mean of at least 3 measurements at 1 metre below surface, mid-depth and 1 metre above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 milligrams per litre within 2 metres of the seabed for 90% of the sampling occasions during the year. (E.R. 5 of 2019) | Marine waters excepting Fish Culture Subzones | |||
| (b)The dissolved oxygen level should not be less than 5 milligrams per litre for 90% of the sampling occasions during the year; values should be calculated as water column average (arithmetic mean of at least 3 measurements at 1 metre below surface, mid-depth and 1 metre above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 milligrams per litre within 2 metres of the seabed for 90% of the sampling occasions during the year. | Fish Culture Subzones | |||
| (c)Waste discharges shall not cause the level of dissolved oxygen to be less than 4 milligrams per litre. | Inland waters of the Zone | |||
| D. | pH | |||
| (a)The pH of the water should be within the range of 6.5–8.5 units. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.2 units. | Marine waters excepting Bathing Beach Subzones; Mui Wo (A), Mui Wo (B), Miu Wo (C), Mui Wo (E) and Mui Wo (F) Subzones. | |||
| (b)The pH of the water should be within the range of 6.0–9.0 units. | Mui Wo (D) Subzone and other inland waters. | |||
| (c)The pH of the water should be within the range of 6.0–9.0 units for 95% of samples. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.5 units. | Bathing Beach Subzones | |||
| E. | TEMPERATURE | |||
| Waste discharges shall not cause the natural daily temperature range to change by more than 2.0 degrees Celsius. | Whole Zone | |||
| F. | SALINITY | |||
| Waste discharges shall not cause the natural ambient salinity level to change by more than 10%. | Whole Zone | |||
| G. | SUSPENDED SOLIDS | |||
| (a)Waste discharges shall neither cause the natural ambient level to be raised by 30% nor give rise to accumulation of suspended solids which may adversely affect aquatic communities. | Marine waters | |||
| (b)Waste discharges shall not cause the annual median of suspended solids to exceed 20 milligrams per litre. | Mui Wo (A), Mui Wo (B), Mui Wo (C), Mui Wo (E) and Mui Wo (F) Subzones. | |||
| (c)Waste discharges shall not cause the annual median of suspended solids to exceed 25 milligrams per litre. | Mui Wo (D) Subzone and other inland waters. | |||
| H. | AMMONIA | |||
| The ammonia nitrogen level should not be more than 0.021 milligram per litre, calculated as the annual average (arithmetic mean), as unionised form. | Whole Zone | |||
| I. | NUTRIENTS | |||
| (a)Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants. | Marine waters | |||
| (b)Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.1 milligram per litre, expressed as annual water column average (arithmetic mean of at least 3 measurements at 1 metre below surface, mid-depth and 1 metre above seabed). | ||||
| J. | 5-DAY BIOCHEMICAL OXYGEN DEMAND | |||
| Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 5 milligrams per litre. | Inland waters of the Zone | |||
| K. | CHEMICAL OXYGEN DEMAND | |||
| Waste discharges shall not cause the chemical oxygen demand to exceed 30 milligrams per litre. | Inland waters of the Zone | |||
| L. | DANGEROUS SUBSTANCES | |||
| (a)Waste discharges shall not cause the concentrations of dangerous substances in marine waters to attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms, with due regard to biologically cumulative effects in food chains and to toxicant interactions with each other. | Whole Zone | |||
| (b)Waste discharges of dangerous substances shall not put a risk to any beneficial uses of the aquatic environment. | Whole Zone | |||
In this Statement— (E.R. 5 of 2019)
bathing beach subzone (泳灘分區) means— (a)a bathing beach that is specified in the Fourth Schedule to the Public Health and Municipal Services Ordinance (Cap. 132) and situated in the Southern Water Control Zone; and (b)the bathing beach at Discovery Bay, which is delineated and coloured in blue on a plan marked SWCZ/DB, signed by the Secretary for Health and Welfare and deposited in the Land Registry; (8 of 1993 s. 30; 21 of 2024 s. 78) fish culture subzone (魚類養殖分區) means a fish culture zone that is designated in the Fish Culture Zone (Designation) Order (Cap. 353 sub. leg. B); (E.R. 5 of 2019) Map (地圖) means the map comprising 7 sheets and marked from SWCZ/Sheet 1 of 7 to SWCZ/Sheet 7 of 7, signed by the Secretary for Health and Welfare on 18 July 1988 and deposited in the Land Registry; (8 of 1993 s. 30; E.R. 5 of 2019; 21 of 2024 s. 78) marine waters (海洋水域) means waters within the Southern Water Control Zone boundary below the high water mark; Mui Wo (A) Subzone (梅窩(A)分區) means all that area bounded by the river catchment boundary in the west, and by a line between a point north of Tseng Tau San Tsuen (22º16'26"N, 113º59'02"E) and a point east of Lung Mei Hang (22º16'16"N, 113º59'05"E) in the east, which is delineated and marked MW(A) on the Map, and which includes the areas of Lin Fa Shan, Lung Mei Tsuen and Lung Mei Hang; Mui Wo (B) Subzone (梅窩(B)分區) means all that area bounded by the river catchment boundary in the south west, and by a line between a point south of Tseng Tau San Tsuen (22º16'19"N, 113º59'04"E) and Tsoi Yuen Tsuen (22º16'12"N, 113º59'13"E) in the east, which is delineated and marked MW(B) on the Map, and which includes the areas of Mui Wo Kau Tsuen, part of Tseng Tau San Tsuen and part of Tsoi Yuen Tsuen; Mui Wo (C) Subzone (梅窩(C)分區) means all that area bounded by the river catchment boundary in the south, and by a line between Tsoi Yuen Tsuen (22º16'12"N, 113º59'13"E) and a point east of Tai Tei Tong (22º16'02"N, 113º59'32"E), which is delineated and marked MW(C) on the Map, and which includes the areas of Luk Tei Tong and Lai Chi Yuen Tsuen; Mui Wo (D) Subzone (梅窩(D)分區) means all that area bounded by a line between a point west of Chung Hau (22º16'14"N, 113º59'31"E) and a point north of Lai Chi Yuen Tsuen (22º15'34"N, 113o59'54"E) in the west, and by the river catchment boundary in the east, which is delineated and marked MW(D) on the Map, and which includes the areas of Chung Hau and the Water Treatment Works; Mui Wo (E) Subzone (梅窩(E)分區) means all that area bounded by a line between a point north of Tseng Tau San Tsuen (22º16'26"N, 113º59'02"E) and a point south of Tseng Tau San Tsuen (22º16'19"N, 113º59'04"E) in the west, and by a line between a point east of Pak Ngan Heung (22º16'19"N, 113º59'31"E) and a point east of Tai Tei Tong (22º16'02"N, 113º59'32"E) in the east, which is delineated and marked MW(E) on the Map, and which includes the areas of Tai Tei Tong, part of Tseng Tau San Tsuen and part of Tsoi Yuen Tsuen; Mui Wo (F) Subzone (梅窩(F)分區) means all that area bounded by the river catchment boundary in the north west and east, and by a line between a point east of Pak Ngan Heung (22º16'19"N, 113º59'31"E) and a point north of Lin Fa Shan (22º16'32"N, 113º58'00"E), which is delineated and marked MW(F) on the Map, and which includes the areas of Mong To Au, A Po Long, Wo Sheung Au, Wong Kung Tin, Wo Tin and Pak Ngan Heung; other inland waters (其他內陸水域) means inland waters other than those in the Mui Wo (A), Mui Wo (B), Mui Wo (C), Mui Wo (D), Mui Wo (E) and Mui Wo (F) Subzones; Secondary Contact Recreation Subzone (次級接觸康樂活動分區) means an area delineated as such on the Map.