Floodwater topped a highway protecting the Bolivian city of Trinidad on Tuesday, threatening to inundate 95,000 residents already suffering from severe flooding in the Amazon region.

The leftist government of President Evo Morales decreed a national disaster, as residents of Trinidad feared the floods could break the dike and wash away parts of their city.

Floods have forced thousands of people from their homes and killed at least 51 people nationwide since November, destroying crops and roadways as well. The unusually heavy rains are blamed on the La Nina weather phenomenon in the Pacific Ocean.

Tent cities have been set up in and around Trinidad, about 310 miles (500 km) northeast of La Paz.

Francisca Ferrufino said she and six relatives had to flee their house nearly a month ago when flooding began to affect the low-lying, poor outskirts of Trinidad.

There's not enough drinking water to go around and food supplies have become scarcer and more expensive, she said.

"There are many people who are sick right now with colds and diarrhea because of the polluted water and because they're still trying to gets their things out from inside (flooded homes)," Ferrufino said.

Some 80,000 square km (30,890 sq mile) are under water in the Amazonian province of Beni, an area roughly the size of Austria.

Local radio station Patuju reported that officials believed the waters covering parts of the dike around Trinidad would stop rising in the next two or three days.

"Since the dike was built 25 years ago, this is the first time waters have risen above it," said Juan Carlos Zambrana, director of the radio station.

The main fear is that the dike could burst allowing water to pour into the city.

"If the dike breaks or is surpassed by floodwater, the disaster would be unfathomable," Trinidad's mayor, Moises Shiriqui, told reporters on Monday, adding that flooding had affected at least 25,000 people in the region.

The city, located 508 feet (155 meters) above sea level, was founded in the 18th century by Spanish Jesuits and is the capital of a cattle-ranching province.