The Panama Canal Authority has tightened restrictions on the largest ships using the waterway – one of the world’s busiest trade routes – due to shallow water levels caused by drought conditions, Reuters reported.

The measure followed a series of depth restrictions in the 80km canal since the beginning of the year due to a drought, which authorities had hoped would ease by the start of the Central American country’s rainy season, the 22 June report said.

Ship traffic, including container ships and oil tankers, using the canal between the Atlantic and Pacific Oceans accounts for around 3.5% of global trade, according to the report.

Introduced on 25 June, the new restrictions limited neo-Panamax container ships to a depth limit of 43.5ft (13.3m) – compared to the maximum draft of 44ft (13.4m) – which meant they must either carry less cargo or reduce their weight, Reuters wrote.

Panamax ships, which use the canal’s older locks, were also expected to face tighter rules from 9 July, the port administration told clients in an advisory seen by Reuters.

Both classes would also see a further limit applied on 19 July, the report said.

Port administrator Ricaurte Vasquez was quoted as saying the 19 July measure would depend on the volume of rainfall entering the lake system surrounding the canal.

El Niño weather patterns had brought a severe drought along the Pacific coast, the report said.

Although new restrictions had been introduced to limit ships’ weight, Vasquez said the flow of ships through the canal had continued as expected to date.

However, the flow of ships could be affected by levels of rainfall and higher route costs due to the new limits, he added.

The new limits would not affect liquefied natural gas (LNG) carriers, as they typically reported drafts of up to 37ft (11.3m), according to the canal authority.