This poem is not about William McGonagall but it was partly inspired by his best line (I think) about the ‘silvery Tay’ and is set by the river where I saw these three guys one day.

Silhouetted against a silver river,
haunted unawares by
handloom and tale spinning weavers,
the scaffolder scurries ant like
on the roof in the wake of the dawn.

A brother woollen hat
appears above the parapet
on grey sullen slates,
fanned by a winnowing breeze
bestowing fallen leaves.

Mid river silver fuses with blue.
A third soldier ant emerges
defying vertigo with silent panache,
impervious to the predator oblivion
who stalks the ground below.