The sad truth is that efforts to prevent the spread of invasive plants in Maine, especially the ones that infest waterways, will likely only slow their march into the state, not stop their spread. When all it takes to start the process of choking a lake with alien green stuff is a one- inch piece of that stuff stuck on someone's propeller, success is measured in small victories.

Yet because invasive plants are a scourge that will hurt Maine's landscape, our recreational opportunities and even our property values, we have to fight them. Who wants to live, paddle or fish on a lake filled with ropy, green milfoil? Invasive plants have been found in only 29 locations in Maine so far, so there's still a lot to protect.

That's why the new boat launch on Messalonskee Lake in Sidney is a welcome thing. The old launch was on Route 27 in a portion of the lake colonized by milfoil. That was a clear threat to other lakes, because boats leaving Messalonskee could carry a hitchhiking piece of plant away with them and transfer it into the next lake into which they were launched. The logical thing to have done years ago, when the infestation was discovered, was to have closed the launch site. But certain politically powerful sportsmen's interests objected because they said the move would threaten their tradition of free access to the lake.

Much controversy attended the discussion about what to do, and while the launch was kept open longer than was wise, it's now closed. And yesterday, the new site was formally opened, at a cost of $590,000 to the state.

That's a lot of money for a boat launch. But consider it this way: It's an insurance payment for our waterways, an investment in keeping them as healthy and free of alien plants as possible. Looked at from that perspective, it seems like money well spent on the interests of all of us in Maine.