The Panama Canal Authority says it will impose new restrictions that will affect how much cargo ships can carry through the major seaway because drought has lowered water levels in Gatun and Alajuela lakes.
Starting Sept. 8, the maximum allowed transit draught will be reduced to 11.89 metres The draught is the vertical distance between the water line and the bottom of a ship's hull.
"The maximum authorized transit draught is the deepest point of immersion in tropical fresh water permitted for a particular vessel in Gatun Lake," the authority said in an advisory issued Aug. 7.
Gatun Lake is a body of water in the midsection of the Panama Canal that ships must pass through.
Although the new restriction takes effect next month, some vessels will have to start making adjustments as early as next week.
"Ships loaded on or after Aug. 11, 2015, must comply with the restriction and may be required to trim or off-load cargo," the authority said.
The draught restriction might be tightened further on Sept, 15 to 11.73 metres, depending on rainfall and lake levels. The authority said in an earlier advisory that restrictions would be imposed in 15 cm increments and announced at least five weeks in advance.
The restriction is the first such hold-down because of weather in nearly 20 years and had been expected by shippers.
Rainfall over the watershed feeding Gatun Lake and Alajuela Lake, which lies east of the canal, has fallen sharply as a result of the El Nino weather phenomenon, lowering the lake levels. Similar problems occurred in 1997-98.
The El Nino phenomenon is linked to the periodic increase in sea-surface temperatures across the tropical Pacific and can alter rainfall patterns, causing an abundance in some regions and a drought in others.
Only about five or six of the 36 ships now using the canal daily will be affected, the authority said.
A previous version of this story said the Panama Canal Authority is limiting the size of ships using the seaway. In fact, it is only limiting the draught, the distance between the water line and a ship's hull, which is related to how much cargo the ship is carrying.Aug 08, 2015 4:04 PM ET