Submerged aquatic plant communities are assessed using the nationally accepted LakeSPI (Submerged Plant Index) methodology developed by Clayton and Edwards (2006). This involves scuba divers assessing 11 metrics over a 2 m wide transect from the shore to the deepest vegetation limit at several sites which are representative of the lake.
The first LakeSPI surveys were carried out in autumn 2011 and are intended to be repeated at five-yearly intervals except where more frequent surveys are warranted.
Application of the LakeSPI method results in three indices expressed as a percentage of expected pristine state:
The LakeSPI index is used to place the lake vegetation into one of five categories of lake condition listed in the table below (Verburg et al. 2010):
| Lake ecological condition | LakeSPI index (% of expected pristine state) |
|---|---|
| Non-vegetated | 0 |
| Poor | >0-20 |
| Moderate | >20-50 |
| High | >50-75 |
| Excellent | >75 |
Each sub-component condition index is also rated against National Policy Statement for Freshwater Management 2020 NOF guidelines:
| Attribute state | Native Condition index | Invasive Impact index |
|---|---|---|
| A | >75 | 0* |
| B | >50 and >75 | >1 and >25 |
| C | >20 and >50 | >25 and >90 |
| D | ≤20 | ≥90 |
*Note Invasive Impact index scores for non-vegetated lakes are not included in the A band.