By Massachusetts law, Spy Pond is defined as a “Great Pond.” But to those who are well acquainted with the pond, it’s not as great as it used to be.

I became a Spy Pond watcher five years ago, when I moved to a house in Arlington that has a view of the pond — an especially good view if you happen to be perched on the apex of our roof. We’re a few houses up from the shoreline on a quiet dead-end street. Instead of hearing the hum of traffic on a still night we hear the honking of geese.

At the end of our street there are concrete steps that lead down to the pond. From there, a path goes along the pond’s edge and over to the Boys and Girls Club. Nearby is the Minuteman Trail, a former railroad line now used by bicyclists, roller-bladers, and pedestrians. It takes you to the Alewife train station. When the weather is good, that’s how I get to work.

One day this spring, as I was walking along the pond path, I came to a low spot where an outfall pipe from under the street empties into the pond. In front of the pipe, I saw a sheen of bluish oil on the surface of the water. I stopped to stare. Why would oil be running into the pond? Is it the natural result of having streets and cars nearby? Or is it something worse? Did some Saturday mechanic in the neighborhood change the oil in his car and then dump the waste into the nearest sewer grate? The thought put me in a foul mood.

A great deal of pollution is unnoticed. You can’t usually see fine particulates in the air. You can’t see leachate (“garbage juice”) seeping from a landfill into the groundwater. If nasty chemicals are put into barrels and hidden underground, we like to think they are “disposed of.” There is a side of us that really does not want to know about it. All those activists running around with horror stories about toxic waste… They seem determined to ruin your day. I made no investigation of where the oil came from.

ell, this was no Exxon Valdez spill on Spy Pond. But seeing even minor pollution up close can be upsetting. All the more when you already suspect things are getting worse, not better. This is how most of us who live near Spy Pond feel about it. We get reports that trace amounts of arsenic are found in the pondwater. But who knows? Arsenic occurs in nature. And you can’t see it or smell it. All the little sunfish I see in the shallow water seem to be doing fine. There are turtles, muskrats, coots, mallards, swans, and geese keeping themselves busy.

The phosphate problem is believable, though. Each summer there are more aquatic weeds. They are taking over the pond, giving the surface a scummy look. They are a sign that the pond is dying — and the chief culprit seems to be the phosphate fertilizers people put on their lawns. The chemicals run off into the pond and fertilize the weeds. Regular leafletting warns homeowners about the problem. But people like their lush, green lawns.

Then there are the Canada geese. Talk about an immigration problem! These big black-collared birds have decided they like it so much here they have taken up permanent residence. They are proliferating like mad. There have been times when I have tried to chase them off Spy Pond Field, waving my hat and flapping my arms. It wasn’t dignified behavior. Nor was it effective.

Quite a debate has broken out in Arlington, as in other towns, about whether people should feed the geese. Those who object to the considerable amounts of goose waste in the pond and along the shore have posted signs saying, “Please don’t feed the geese.” Goose-lovers have ripped the signs down.

On a bulletin board near Spy Pond, someone answered the anti-geese activists with a page-long appeal to reason, entitled “Please feed the geese.” The point was that the water quality would not improve measurably if people refrained from feeding the birds. The problem, he or she argued, is not the geese — it’s the humans. Take away the streets and cars and lawns and playing fields from the immediate area and the problem would be solved. In the meantime, don’t take your frustration out on the geese, or on the geese-feeders.

Someone responded in the margin: “Once upon a time we swam in this pond without goose poop.” And, one might add, without the weeds and the oil and the arsenic.

The geese are only the most visible sign that things are out of balance. I’m annoyed with them, too. But it really isn’t their fault.