Hemlock? A weed on Merri Creek
Very common around here
Oddly, while hemlock was dominant on the terrace on the other side of the Rakaia River, there was none on the side of the river we were on (the northern side). I had a good look.
Conium maculatum, large plant in early stage of growth
Conium (/koʊˈnaɪ.əm/ or /ˈkoʊniəm/) is a genus of one or two species of highly poisonous perennial herbaceous flowering plants in the family Apiaceae, native to Europe and the Mediterranean region as Conium maculatum (known popularly as Hemlock), and to southern Africa as Conium chaerophylloides.