SAO PAULO (AP) — A severe drought has dropped water levels on a major Amazon tributary to their lowest point since officials began keeping records more than a century ago, the government reported Monday, cutting off dozens of communities who depend on the river for work and transportation.

Floating homes along the Rio Negro now rest on muddy flats, and locals have had to modify boats to run in shallower waters in a region without roads. Some riverbanks have caved in, although no injuries have been reported.

The drought is hurting fishing, cattle, agriculture and other businesses, prompting authorities to declare a state of emergency in nearly 40 municipalities. Authorities did not say how many people are affected, but Brazilian media estimated that some 60,000 families live in the area.

“It is a difficult situation for the community,” resident Josimar Peixoto told Globo TV. “The families are struggling here.”

The government’s geological service said Monday that the Rio Negro was measured at a depth of 13.63 meters (44.72 feet) the previous day near the jungle city of Manaus, the lowest since a measuring system was implemented in 1902.

Manaus, in northern Brazil, is where the Rio Negro is at its deepest and where it merges with the Amazon River — meaning some places upstream are nearly completely dry.

The previous low was 13.64 meters (44.75 feet), recorded in 1963.

An engineer and hydrology expert with the geological service said rains in remote parts of the Amazon will begin raising river levels, but it will take time for that water to reach Manaus.

“The water is expected to start rising again in about three to four weeks,” Daniel Oliveira told The Associated Press.

Early last year, the Rio Negro hit a record high of 29.71 meters (97.5 feet) near Manaus following months of heavy rains.

The government has distributed about 600 tons of food, water and medicine to people affected by the drought.

• TALES AZZONI