Beyond ruining a perfectly good soccer pitch, the kilogram of daily droppings a single adult Canada goose can produce can also contaminate water and cause algae blooms that steal oxygen and block sunlight for underwater plants. Local birder Geoffrey Newell said they can also be aggressive birds and sometimes steal food from ducks and other goose species. He noted this doesn’t apply to Canada geese fully native to B.C., which migrate to the Arctic in winter.