The Calder & Hebble Navigation is a mixed canal and river navigation, length c.38km, linking Wakefield and Sowerby Bridge (Anon, 2009). The Navigation is not widely celebrated for the conservation value of its aquatic plant communities. This contrastswith other trans-Pennine canal routes: the Leeds & Liverpool Canal, the Huddersfield Narrow Canal and the Rochdale Canal (that continues the route of the Calder & Hebble) all have sections that are designated as SSSIs because of the richness of their aquatic vegetation (Natural England, 2015). Features of botanical importance have, however, been reported from some canal sections of the Calder & Hebble Navigation. For example, the rare American Pondweed1, which was first recorded as a native plant in the Outer Hebrides in 1943, has been known in the Calder & Hebble and regarded as an alien plant since 1907 (Preston & Croft, 1997) and was still there in 2011 (Goulder, 2013a). Floating Water-plantain and Hairlike Pondweed, both listed as scarce plants in Britain by Preston & Croft (loc. cit.) and the former being specially protected throughout Europe, were to be found in the Calder & Hebble in 2011-2012 (Goulder, 2013a).
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