Five indices are used to investigate the whole picture of a river environment, including the river water, the living things, the scenery, and its use in our daily lives. Each index has three to five items (called separate indicators) used to investigate the river condition.
Evaluate each separate indicator on a scale of 3 to 1 by observing the river conditions.
If possible, write the reasons why you chose your ranking.
You can start with any indicator that seems appropriate.

3. Water clarity

This represents how clean and clear the water is.

*For more detailed information,
please refer to the Ministry of the Environment manual "Let's go to a river together! (PDF)".

(1) Transparency

Is the water clear?

Transparency is a visual parameter indicating how clear the water is. Let’s measure it using a transparency tube. When a transparency tube is not available, you can make one using an acrylic tube.

Scale Transparency
3 More than 70 cm
2 More than 50 cm but less than 70 cm
1 Less than 50 cm

Measuring water clarity using a transparency meter

(2) Smell of the water

Does the water smell?

By investigating the smell of the water, we can identify the effect of wastewater. Place a water sample in a container and shake it. Bring your nose close to the container and sniff it. When it is difficult to take a water sample, stand near the riverside and sniff the air.

Scale Smell of the water
3 No smell
2 A slight smell
1 A very bad smell

(3) COD (Chemical oxygen demand)

Is the water clean?

COD (Chemical Oxygen Demand) is a parameter used to investigate the level of water pollution by organic substances. This is optional and is for those who are interested in this item.

Scale COD
3 Less than 3 mg/l
2 Between 3 mg/l and 5 mg/l
1 More than 5 mg/l

All photos shown here are of rivers in Japan. When the number of overseas surveys increases in the future, we plan to present photos of overseas rivers here. We hope that with your cooperation, surveys will be conducted widely around the world.

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