Ecological potential - assessing heavily modified and artificial waters

Knowledge base · July 7, 2026

When reading water assessments, you may come across a term that surprises many: instead of “ecological status”, ecological potential appears. This is no mistake - some waters are assessed by a slightly different measure, because they have been physically modified to a degree that changes the reference point. It is worth understanding this difference so as not to compare “apples with pears”.

Heavily modified and artificial waters

• Heavily modified water bodies (HMWB) are water bodies whose character has been substantially changed by human activity - e.g. regulated rivers, dam reservoirs - in a way connected with an important use (flood protection, energy, navigation, water supply).
• Artificial water bodies (AWB) are waters created by people where they did not exist before - e.g. canals.

In both cases, restoring a state close to natural is not possible without giving up that use - which is why they are assessed differently.

Why potential, not status

For such waters the reference point is not a natural river or lake but the best state achievable given the particular alteration - the so-called maximum ecological potential. The water body is assessed by how close it is to this. Hence we speak of potential, not of status.

The scale

Ecological potential is described in classes analogous to status:

• maximum,
• good,
• moderate,
• poor,
• bad.

Chemical status, on the other hand, is assessed in the same way as for natural waters (good / failing to achieve good) - physical alteration does not change the chemical criteria. The environmental objective for these waters is usually good ecological potential and good chemical status.

In practice

From the point of view of someone running monitoring, the measurement methodology itself does not change - the difference lies in the interpretation of the results against the appropriate reference point. Whether a water body is natural, heavily modified or artificial, you can check by its category in the JCWP (see water bodies - JCWP). The measurements themselves are still worth keeping organised - e.g. in a LimnoLog project, with guidelines for the indicators. On how potential and status combine into the overall assessment, we describe in the article Classes and status of water quality.