Wastewater Treatment Plant Bypass Reports

To protect a wastewater treatment plant’s ability to continue treating wastewater during heavy rain or snow melt, some of the excess flow (stormwater and sewage) that reaches the plant may need to be diverted around the secondary treatment process (biological treatment using microorganisms).

Because the bypass process happens during heavy rain or snow melt, the bypassed water is mostly stormwater (often a ratio of four or five parts stormwater to one part sewage). All bypass flow still goes through:

  • screening
  • grit removal
  • primary treatment
  • phosphorous removal
  • disinfection

Bypasses can occur at the Ashbridges Bay and Humber Treatment Plants, as these plants service older areas of the city with combined sewers (one pipe that carries stormwater and sewage).

The bypass reports are updated monthly, within 30 days of the end of each month.

Ashbridges Bay Treatment Plant Bypasses (2026)
Date Duration (hrs) Volume (m3) Reason
January 6-7 4.5469 162,360 Excessive stormwater flow
February 20 7.0172 251,380 Excessive stormwater flow
March 7-8 14.7519 342,720 Excessive stormwater flow
March 11-12 13.5355 307,250 Excessive stormwater flow
March 20 4.5064 169,590 Excessive stormwater flow
March 22 3.8125 145,790 Excessive stormwater flow
March 31 - April 1 8.0477 351,990 Excessive stormwater flow
April 4-5 3.5375 112,690 Excessive stormwater flow
April 14 4.5783 176,810 Excessive stormwater flow
April 15-16 12.3234 411,150 Excessive stormwater flow
April 25 9.7681 249,890 Excessive stormwater flow
May 13 2.8431 80,990 Excessive stormwater flow
May 23-24 17.3719 991,890 Excessive stormwater flow
June 14 6.3303 212,340 Excessive stormwater flow
June 18 13.9925 716,060 Excessive stormwater flow
July 4 2.8481 49,240 Excessive stormwater flow
July 9 1.6247 32,710 Excessive stormwater flow
Humber Treatment Plant Bypasses (2026)
Date Duration (hrs) Volume (m3) Reason
March 31 2.3 35,148 Excessive stormwater flow
April 15 6.4 27,176 Excessive stormwater flow
June 18 8.8 58,488 Excessive stormwater flow
Ashbridges Bay Treatment Plant Bypasses (2025)
Date Duration (hrs) Volume (m3) Reason
March 5 10.3206 251,770 Excessive stormwater flow
March 16 6.7083 126,320 Excessive stormwater flow
April 2 - 3 24.0419 1,211,680 Excessive stormwater flow
May 21 - 23 28.2053 1,082,800 Excessive stormwater flow
July 13 0.4747 22,190 Excessive stormwater flow
July 20 4.9989 179,770 Excessive stormwater flow
August 20 2.6842 115,860 Excessive stormwater flow
September 9 1.1144 50 Planned maintenance
September 21 - 22 6.7066 262,430 Excessive stormwater flow
September 25 6.2922 204,590 Excessive stormwater flow
October 19 2.0856 30,870 Excessive stormwater flow
November 30 4.8833 127,240 Excessive stormwater flow
December 28 - 29 10.2408 676,150 Excessive stormwater flow
Humber Treatment Plant Bypasses (2025)
Date Duration (hrs) Volume (m3) Reason
March 5 1.4 8,195 Excessive stormwater flow
March 16 8.5 49,016 Excessive stormwater flow
April 2 18.5 188,593 Excessive stormwater flow
May 16 0.7 5,000 Excessive stormwater flow
July 20 2.8 27,048 Excessive stormwater flow
September 24 2.7 46,550 Excessive stormwater flow
December 28 5.8 92,853 Excessive stormwater flow
Ashbridges Bay Treatment Plant Bypasses (2024)
Date Duration (hrs) Volume (m3) Reason
January 9 - 10 9.766 415,000 Excessive stormwater flow
January 13 6.583 135,410 Excessive stormwater flow
January 26 9.767 346,000 Excessive stormwater flow
February 27 - 28 7.5833 290,330 Excessive stormwater flow
March 9 6.9166 128,940 Excessive stormwater flow
March 14 - 15 4.5 178,910 Excessive stormwater flow
April 3 - 4 37 1,605,810 Excessive stormwater flow
April 12 - 13 17.7833 473,700 Excessive stormwater flow
April 14 5.1 88,680 Excessive stormwater flow
April 18 2.5833 107,530 Excessive stormwater flow
May 27 12.7119 468,040 Excessive stormwater flow
June 7 2 61,140 Excessive stormwater flow
June 20 3.6166 90,000 Excessive stormwater flow
June 29 4.4333 170,720 Excessive stormwater flow
July 10 10.4333 477,960 Excessive stormwater flow
July 15 5.2 222,510 Excessive stormwater flow
July 16 11.7666 859,900 Excessive stormwater flow
July 24 3.2166 135,880 Excessive stormwater flow
August 5 6.25 266,000 Excessive stormwater flow
August 17 - 18 6.65 239,320 Excessive stormwater flow
September 10 0.7833 50 Planned maintenance
September 23 4.9 200,080 Excessive stormwater flow
September 25 2.3666 55,740 Excessive stormwater flow
November 20 - 21 4.4175 196,930 Excessive stormwater flow
December 16 - 17 2.7722 71,100 Excessive stormwater flow
December 29 7.1317 270,290 Excessive stormwater flow
Humber Treatment Plant Bypasses (2024)
Date Duration (hrs) Volume (m3) Reason
January 9 5.8 23,006 Excessive stormwater flow
January 26 4.5 16,455 Excessive stormwater flow
April 3 15.8 117,032 Excessive stormwater flow
April 11 23.8 80,517 Excessive stormwater flow
May 27 3 32,028 Excessive stormwater flow
July 10 17.2 28,562 Excessive stormwater flow
July 15 2.8 16,981 Excessive stormwater flow
July 16 16 381,514 Excessive stormwater flow
August 17 10 255,411 Excessive stormwater flow
September 23 4.7 45,568 Excessive stormwater flow
December 29 10.6 82,381 Excessive stormwater flow
Ashbridges Bay Treatment Plant Bypasses (2023)
Date Duration (hrs) Volume (m3) Reason
January 4 5.3416 267,090 Excessive stormwater flow
February 9 to 10 14.5566 745,270 Excessive stormwater flow
March 25 8.95 427,060 Excessive stormwater flow
April 1 6.866 351,060 Excessive stormwater flow
April 5 9.575 453,980 Excessive stormwater flow
April 22 8.85 248,820 Excessive stormwater flow
May 20 6.6833 208,350 Excessive stormwater flow
June 12 12.6 758,740 Excessive stormwater flow
July 13 5.516 183,610 Excessive stormwater flow
July 27 3.092 128,310 Excessive stormwater flow
July 29 3.325 105,660 Excessive stormwater flow
August 25 1.4833 35,740 Excessive stormwater flow
September 14 0.65 50 Annual planned maintenance
November 8 to 9 4.48333 90,660 Excessive stormwater flow
November 21 3.95 102,040 Excessive stormwater flow
December 17 5.233 92,510 Excessive stormwater flow
December 27 6.683 395,720 Excessive stormwater flow
Humber Treatment Plant Bypasses (2023)
Date Duration (hrs) Volume (m3) Reason
January 4 6.0 72,890 Excessive stormwater flow
February 17 13.4 65,174 Excessive stormwater flow
March 17 11.1 67,795 Excessive stormwater flow
March 25 11.7 112,948 Excessive stormwater flow
April 1 11.1 41,006 Excessive stormwater flow
April 05 12.4 101,625 Excessive stormwater flow
April 22 2.6 12,894 Excessive stormwater flow
April 30 4.8 28,012 Excessive stormwater flow
May 5 3.5 37,390 Excessive stormwater flow
June 12 9.8 235,572 Excessive stormwater flow
June 26 0.1 312 Excessive stormwater flow
June 27 2.4 13,241 Excessive stormwater flow
July 13 3.8 15,249 Excessive stormwater flow
July 23 1.4 3.462 Excessive stormwater flow
July 27 2.6 19,203 Excessive stormwater flow
July 29 3.3 19,604 Excessive stormwater flow
September 7 0.8 1,926 Excessive stormwater flow
Ashbridges Bay Treatment Plant Bypasses (2022)
Date Duration (hrs) Volume (m3) Reason
February 2 2.9166 50,140 Excessive stormwater flow
February 17 12.7666 591,830 Excessive stormwater flow
February 22 3.6166 111,810 Excessive stormwater flow
June 7 7.6333 291,650 Excessive stormwater flow
July 18 5.1666 208,520 Excessive stormwater flow
August 22 7.2 199,610 Excessive stormwater flow
October 13 1.42 27,660 Excessive stormwater flow
November 8 1.683 41 Annual planned maintenance
November 11 4.133 52,150 Excessive stormwater flow
November 30 7.649 220,430 Excessive stormwater flow
December 15 to 16 22.2666 636,910 Excessive stormwater flow
December 23 8.4964 232,650 Excessive stormwater flow
December 31 9.2333 235,370 Excessive stormwater flow
Humber Treatment Plant Bypasses (2022)
Date Duration (hrs) Volume (m3) Reason
February 17 15.183 191,452 Excessive stormwater flow
February 22 4.033 12,433 Excessive stormwater flow
March 23 3.25 35,586 Excessive stormwater flow
July 24 0.65 4,127 Excessive stormwater flow
December 31 1.1 1,153 Excessive stormwater flow
Ashbridges Bay Treatment Plant Bypasses (2021)
Date Duration (hrs) Volume (m3) Reason
March 26 6.7433 305,870 Excessive stormwater flow
June 29 0.43 6,800 Excessive stormwater flow
July 8 3.82 216,480 Excessive stormwater flow
August 24 2.26 31 Annual planned maintenance
September 8 3.5 153,320 Excessive stormwater flow
September 22 to 23 7.56 245,240 Excessive stormwater flow
October 30 5.59 224,660 Excessive stormwater flow
December 5 3.4833 122,220 Excessive stormwater flow
Humber Treatment Plant Bypasses (2021)
Date Duration (hrs) Volume (m3) Reason
March 26 3.0 31,663 Excessive stormwater flow
May 2 0.33 1,390 Power/Equipment Failure
June 29 2.3 27,465 Excessive stormwater flow
July 8 3.75 26,563 Excessive stormwater flow
August 28 1.5 7,058 Excessive stormwater flow
September 7 2.5 6,750 Excessive stormwater flow
September 8 2.9 36,141 Excessive stormwater flow
September 15 1.8 13,060 Excessive stormwater flow
September 22 0.8 579 Excessive stormwater flow
September 22 7.0 128,486 Excessive stormwater flow
October 15 1.7 15,870 Excessive stormwater flow
December 5 3.0 34,811 Excessive stormwater flow
December 11 2.8 17,547 Excessive stormwater flow
Ashbridges Bay Treatment Plant Bypasses (2020)
Date Duration (hrs) Volume (m3) Reason
January 11 to 12 21.55 807,000 Excessive stormwater flow
January 24 to 25 23.35 1,088,140 Excessive stormwater flow
March 3 4.37 158,890 Excessive stormwater flow
August 2 2.38 86,500 Excessive stormwater flow
November 30 9.217 289,550 Excessive stormwater flow
December 12 2.8 86,510 Excessive stormwater flow
Humber Treatment Plant Bypasses (2020)
Date Duration (hrs) Volume (m3) Reason
January 11 35.8 818,105 Excessive stormwater flow
January 24 9.6 138,795 Excessive stormwater flow
March 3 1.5 29,099 Excessive stormwater flow
July 8 2.7 28,667 Excessive stormwater flow
July 11 1.0 4,664 Excessive stormwater flow
August 2 1.9 14,440 Excessive stormwater flow
August 3 2.1 29,135 Excessive stormwater flow

Bypass information can also be found in the Ashbridges Bay Treatment Plant and Humber Treatment Plant Annual Reports.

Date modified: July 31, 2026