Hawkesbury-Nepean River Environmental Monitoring Program

Dam to Wisemans Ferry. The results of this study are reported by Thiebaud and
Williams (2008) and included in Appendix 9.
Native as well as exotic species were encountered in each of three categories:
submerged, emergent, and floating vegetation. Macrophytes in the submerged
category included the native plants Ceratophyllum demersum, Hydrilla verticillata,
Najas tenuifolia, and Vallisneria gigantea. Two exotic species in this category, Egeria
densa and Elodea canadensis, were also encountered, the former being widespread
in occurrence and of particular concern as it has spoiled the recreational amenity of
the waterway.
Emergent macrophytes included Bolboschoenus fluviatilis, Juncus usitatus,
Phragmites australis, Schoenoplectus validus, Triglochin procerum, and Typha
orientalis. Gymnocoronis spilanthoides and Sagittaria graminea ssp. platyphylla, two
introduced species, had a limited distribution, being found only within the central
portion of the study area.
Native floating macrophytes included Azolla spp., Lemna spp., and Ludwigia
peploides ssp. montevidensis, whereas the introduced Alternanthera philoxeroides,
Eichhornia crassipes and Salvinia molesta were confined to the upper and central
portions of the study area. The latter three species have been of particular concern in
the past.
Figure 6.34: Egeria densa stranded after minor flooding in June 2007 (Photos courtesy
of DPI Fisheries—Thiebaud and Williams 2008)
Major conclusions from Thiebaud and Williams’s (2008) study were:
• Much of the shoreline of the Hawkesbury-Nepean River from Warragamba Dam
to Wisemans Ferry was vegetated with emergent or submerged macrophytes.
• The distribution of the floating macrophytes was restricted to the more central
section of the study area.
• The introduced submerged species Egeria densa was present throughout much
of the study area.
• The introduced submerged species Cabomba caroliniana was not found in the
study area.
64 Hawkesbury Nepean River Environmental Monitoring Program: Final Technical Report