The patient work of Costa Mar's beaches

The beach at Punta Negra was the colour of weak tea when María Sánchez arrived at dawn. She stood at the tide line with a clipboard and a pair of waders, watching her team move through the shallows with nets and buckets. The runoff from the September storms had retreated by then, but the deposit it left behind—a band of dark sediment, fragments of plastic, the occasional styrofoam cooler—remained. Sánchez is the coordinator for the Costa Mar Reef Monitoring Network's northern station, and she has been measuring this particular beach's intake for six months.

The work is unglamorous and incremental. A single morning's haul at Punta Negra last week yielded 47 kilograms of mixed plastic, 12 kilograms of fishing line, and seventeen water samples showing nitrogen levels at 8.2 milligrams per litre—down from 9.1 a month earlier, but still above the 6.5 threshold the Network considers safe for coral. Across Costa Mar's three major beach-cleanup zones, the tallies have become a weekly ritual: the measurement, the recording, the slow arithmetic of recovery.

For Sánchez and the other coordinators, the numbers carry an unspoken tension. The cleanup work is essential, but it is also reactive—a response to runoff and debris that should never have accumulated in the first place. The question that hangs over the work is whether the effort can outpace the sources. The rainy season runs through November, and the nitrogen surge that has plagued the reef for two years shows no sign of abating.