Wastewater Treatment Plant Bypass Reports

In order to protect the wastewater treatment plant’s ability to continue treating wastewater during an extreme rainstorm, some of the excess flow (stormwater and sewage) that reaches the plant may need to be diverted around one of the plant’s many treatment processes.

Because the bypass process happens during storm events, the water is mostly rain water (often a ratio of four or five parts rain to one part sewage). All bypass flow continues to goes through:

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

Bypassses can occur at the Ashbridges Bay and Humber Wastewater 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 (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

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
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
Ashbridges Bay Treatment Plant Bypasses (2019)
Date Duration (hrs) Volume (m3) Reason
February 4 to 5 7.5 165,840 Excessive stormwater flow
February 24 5.3 50,843 Excessive stormwater flow
March 10 7.8 96,750 Excessive stormwater flow
March 14 to 15 2.6 40,120 Excessive stormwater flow
April 14 to 15 3.9 215,650 Excessive stormwater flow
April 19 3.0 58,330 Excessive stormwater flow
April 26 5.2 255,330 Excessive stormwater flow
May 25 2.9 54,980 Excessive stormwater flow
June 13 7.8 163,010 Excessive stormwater flow
June 20 to 21 5.3 189,830 Excessive stormwater flow
June 25 2.4 70,860 Excessive stormwater flow
June 29 2.3 99,220 Excessive stormwater flow
July 13 2.3 94,020 Excessive stormwater flow
July 17 10.2 342,850 Excessive stormwater flow
July 30 5.1 219,230 Excessive stormwater flow
August 17 3.2 51,300 Excessive stormwater flow
August 27 0.41 23,160 Excessive stormwater flow
October 21 6.01 221,400 Excessive stormwater flow
October 27 9.05 342,380 Excessive stormwater flow
October 30 to November 1 16.75 592,510 Excessive stormwater flow
December 9 7.15 256,720 Excessive stormwater flow
December 14 10 526,270 Excessive stormwater flow
*More than one bypass occurred over this total amount of time due to one rain event. Active hours denote the time the bypass process was activated.
Humber Treatment Plant Bypasses (2019)
Date Duration (hrs) Volume (m3) Reason
February 4-5 2.0 2,599 Excessive stormwater flow
March 14-15 7.2 24,383 Excessive stormwater flow
March 30 9.4 (5.4 Active)* 16,555 Excessive stormwater flow
March 31 0.8 1,727 Excessive stormwater flow
Aprill 14 3.5 40,204 Excessive stormwater flow
April 19 1.7 5,419 Excessive stormwater flow
April 20 7.7 (5.0 active)* 16,877 Excessive stormwater flow
April 26 5.3 23,868 Excessive stormwater flow
May 1 2.2 9,520 Excessive stormwater flow
May 3 4.5 10,087 Excessive stormwater flow
May 25 2.7 23,828 Excessive stormwater flow
June 10 0.33 55 Excessive stormwater flow
June 20 3.7 35,985 Excessive stormwater flow
July 17 7.1 69,573 Excessive stormwater flow
August 17 1.4 8,332 Excessive stormwater flow
October 16 1.1 2,920 Excessive stormwater flow
October 27 4.4 42,424 Excessive stormwater flow
October 31 6.25 95,650 Excessive stormwater flow
December 14 2.25 14,228 Excessive stormwater flow
Ashbridges Bay Treatment Plant Bypasses (2018)
Date Duration (hrs) Volume (m3) Reason
January 12 4.25 90,709 Excessive stormwater flow
April 16 to 17 16.95 729,819 Excessive stormwater flow
June 24 4.10 99,410 Excessive stormwater flow
August 7 to 8 3.72 127,350 Excessive stormwater flow
November 1 to 2 7.55 244,510 Excessive stormwater flow
November 26 9.86 264,440 Excessive stormwater flow
*More than one bypass occurred over this total amount of time due to one rain event. Active hours denote the time the bypass process was activated.
Humber Treatment Plant Bypasses (2018)
Date Duration (hrs) Volume (m3) Reason
January 11 to 12 17.6 total (4.7 active)*  13,249 Excessive stormwater flow
February 20 14.9 total (7.6 active)* 14,131 Excessive stormwater flow
February 21 3.3 956 Excessive stormwater flow
April 3 to 4 6.5 31,962 Excessive stormwater flow
April 16 to 18 46.5 332,131 Excessive stormwater flow
April 25 4.6 142,65 Excessive stormwater flow
June 13 0.75 1,200 Excessive stormwater flow
June 24 3.5 23,772 Excessive stormwater flow
July 5 1.5 8,983 Excessive stormwater flow
July 22 0.5 1,377 Excessive stormwater flow
July 24 0.6 325 Excessive stormwater flow
August 6 1.8 11,556 Excessive stormwater flow
August 7 to 8 5.7 35,581 Excessive stormwater flow
August 17 0.8 2,207 Excessive stormwater flow
August 21 3.25 13,499 Excessive stormwater flow
September 10 2.7 1,428 Excessive stormwater flow
October 2 0.2 418 Excessive stormwater flow
November 1 to 2 8.75 43,713 Excessive stormwater flow
November 26 2.5 13,736 Excessive stormwater flow

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