The Freshwater Biological Association ‘Habitat Naturalness Assessment’ is used to assess the condition of lakes. Scores for four attributes (physical, hydrological, chemical, and biological naturalness) are averaged to generate an overall 'habitat naturalness assessment score' which can then be translated into a condition score for use in the metric (see below).
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There are other elements considered in the lake naturalness assessment, but these are not included when calculating the condition assessment score.
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Details of the methodology for assessing naturalness of lakes are available at: Contribute naturalness data – Discovering Priority Habitats in England

The key documents are:

Lake naturalness assessment – guidance document (PDF)

Annex I – Printable lake naturalness survey form to use in field (PDF)

Annex II – Physical naturalness photographs (PDF)

Annex-III - Hydrological naturalness photographs (PDF)

Annex IV – Chemical naturalness photographs (PDF)

Annex V – Plant functional group photographs (PDF)

Annex VI – Further species recording (PDF)

We encourage recording of data on lakes on the Freshwater Biological Association ‘Habitat Naturalness Assessment’ website portal: Contribute data – Discovering Priority Habitats in England (wpengine.com)

Average 'Habitat Naturalness Assessment' Class

Condition Assessment Score

1 Natural

Good (3)

2

Fairly good (2.5)

3

Moderate (2)

4

Fairly poor (1.5)

5 Least natural

Poor (1)

Channels & Challenges: Enhancing Salmonid Rivers. Irish Freshwater Fisheries Ecology & Management Series No. 4. Central Fisheries Board, Dublin.

Pond Creation Toolkit

Translocation of Scirpus triqueter

Illustrated Guide to ponds and scrapes. NE TIN079.

https://www.therrc.co.uk/manual-river-restoration-techniques

Creating ponds for rare mosses and liverworts