Butterbur

I had to look this plant up, and it turns out to be Butterbur (Petasites hybridus). They grow in damp places; these were at the edge of the canal. These pink flower spikes grow before the leaves, which can become huge. (I'd have recognised the leaves.) Apparently, they are in the same family as sunflowers. They have been used medicinally for a long time and extracts are known to be an effective herbal treatment for migraine and some allergies, though potentially adverse long-term effects are not well documented.