Specially trained crews from New York City's Department of Environmental Protection will employ unusual techniques to remove weeds from the face of the 307-foot-high Kensico Reservoir Dam before the invasive plants allow water to seep through the structure, which could weaken it.

Landscape workers are called upon to perform many different tasks so their skillsets are often wide-ranging but how many of them are asked to rappel down steep dam faces?

That is what workers from New York City's Department of Environmental Protection will do in an attempt to eradicate weeds from the face of the Kensico Reservoir Dam in Valhalla, N.Y.

Michael Risinit of the Journal News in White Plains, N.Y., reports that for much of the next few weeks, the top of the dam, which is usually open to foot traffic, will be closed as the work progresses through mid-June.

The specially trained crews will rappel the dam's face and apply herbicide to the weeds growing between the stones of the 307-foot-high dam. According to DEP officials, the plants can allow water to trickle between the stones, possibly damaging the joints and the stone face when it freezes.

The herbicide will be applied for two weeks, followed by a one-week hiatus and then by another two-week application period.

Officials said the herbicide must be applied when the weeds are in bloom. Workers will re-grout the spaces between the stones after the weeds are removed.

Put into service in 1915, the Kensico Reservoir Dam is about 15 miles north of New York City. The Kensico Dam impounds the Bronx River, but the reservoir behind it receives most of its water from other sources, as it is the collecting point for the water from all six reservoirs in the Catskill Mountains.