The rope is back.

For most of the summer a length of dachshund-shaped line has been tied to a cut piling below the seawall, and for the better part of a week in August it was not. It is there again, on the same ledge, at the same height, and it has been working.

Since its return it has caught: one branch, roughly four feet, still leafed. A sheet of plastic film. One can. A quantity of leaves. Two feathers, gray, unidentified.

This is what a boom does. A boom is a floating barrier set across moving water to collect what the water is carrying, and it is ordinary equipment on rivers where somebody has decided the carrying is a problem. Nobody set this one. It was tied there for another reason, or for no reason, and the river has been treating it as infrastructure.

Downstream of the tether the material changes character. Along the granite it arrives in a continuous band, delivered by the water and left at the line the water reaches. Above the granite, on the park side, it is discrete and individual — a filter, a wrapper, a second wrapper — and it did not come from the river. It came from the eighteen inches of mown grass above it. Two mechanisms, one waterline, and only one of them can be blamed on the tide.

Also present: one great blue heron, standing on a WaterFire brazier platform with its wings folded. The platform is whitewashed, which means the heron is not a visitor. A second heron on cut pilings in open water toward India Point. One cormorant, wings out, drying. One blue crab, dead, in the shallows — Callinectes sapidus, the first this column has been able to photograph rather than merely assert.

As to the missing week: the tether is understood to have been in Ward 11, knocking on doors. This column has no comment from the campaign. It has the rope, back on its ledge, holding a branch.