IB ESS SL 4.4.3 Water Quality Measurement Question Bank
Interpret physical, chemical and biological indicators of water quality.
- Syllabus
- First assessment 2026
- Course
- ESS SL
- Level
- SL
Interpret physical, chemical and biological indicators of water quality.

Figure:Coliform bacteria one day after untreated sewage release
Using Figure: Coliform bacteria one day after untreated sewage release, estimate the highest concentrations of coliform bacteria (in units/ 100 mL ) found in the St Lawrence River one day after the untreated sewage was released.
120000 (units / 100 ml );
Units are not required.

Figure:Coliform bacteria before untreated sewage release
- Figure: Untreated sewage release into the St Lawrence River
- Figure: Untreated sewage release into the St Lawrence River: Montreal discharged 5-8 billion litres of untreated sewage into the St Lawrence River in November 2015; river pollution returned to normal within 4-10 days.
- Quebec discharged 110 million litres in November 2016; nationally, 205 billion litres of untreated sewage are released into Canadian rivers and oceans each year.
With reference to Figures: Untreated sewage release into the St Lawrence River, Coliform bacteria before untreated sewage release and Coliform bacteria one day after untreated sewage release, describe a method to monitor the impact of the release of untreated sewage into the St Lawrence River ecosystem.
can use indirect or direct measures of pollution;
direct measurements of dissolved oxygen using a probe / light and dark bottle method to measure BOD / direct counts of coliform units using microscopes / Secchi disc to monitor turbidity / titration to measure changes in nitrates/phosphates; freshwater invertebrates can be used as indicator species;
compare with historic data / take measurements before the release of the untreated sewage (for 'normal' measurements);
take measurements along the length of the river, from the point source downstream (to determine area impacted); take measurements over a period of time, to observe changes in water quality;