The Panama Canal Authority said Friday that next month it will temporarily limit the size of ships using the waterway because drought has lowered water levels in Gatun and Alhajuela lakes.

The restriction, which is the first such hold-down because of weather in nearly 20 years, takes effect Sept. 8 and had been expected by shippers. Only a minority of ships now using the canal will be kept out, the authority said.

Rainfall over the watershed feeding the lakes at the midsection of the waterway has fallen sharply as a result of the El Nino weather phenomenon, lowering the lake levels. Similar problems occurred in 1997-98.

The authority said ships will be limited to a maximum draft of 39 feet (11.89 meters) beginning Sept. 8. It added that the limit might be further reduced to 38.5 feet (11.73 meters) on Sept. 16.

Only about five or six of the 36 ships now using the canal daily will be affected, the authority said.