A mysterious oil spill that has polluted at least 150 beaches along Brazil's northeastern coast reached the city of Salvador on Friday as officials tried to determine the source of the crude sludge.

Authorities confirmed the oil had reached the Piata beach in Salvador, Brazil's fourth-largest city that's known for its beaches and Afro-Brazilian culture. Overall, 68 municipalities in nine states have been affected by the spill that began on Sept. 2.

A report from Brazil's Institute of the Environment and Water Resources said the origin of the sludge has still not been determined, though environment minister Ricardo Salles earlier said the oil was likely of Venezuelan origin — something denied by Caracas. The main hypothesis is that the oil spilled from a vessel passing near the Brazilian coast.

CORRECTS DATE - In this Oct. 7, 2019 handout photo released by the Aracaju Municipal Press Office, workers remove oil from Viral Beach, in Aracaju, Brazil. The oil that has been polluting Brazil's northeastern beaches since early September is likely coming from Venezuela, according to a report by Brazil's state oil company cited by the country's environment minister. The oil sludge has now reached 61 municipalities in nine Brazilian states, contaminating over 130 beaches, in what Brazilian officials have called an "unheard of" disaster. (Andre MoreiraAracaju Municipal Press Office via AP)

CORRECTS DATE - In this Oct. 7, 2019 handout photo released by the Aracaju Municipal Press Office, workers remove oil from Viral Beach, in Aracaju, Brazil. The oil that has been polluting Brazil's northeastern beaches since early September is likely coming from Venezuela, according to a report by Brazil's state oil company cited by the country's environment minister. The oil sludge has now reached 61 municipalities in nine Brazilian states, contaminating over 130 beaches, in what Brazilian officials have called an "unheard of" disaster. (Andre MoreiraAracaju Municipal Press Office via AP)

After studying the ships that passed through the region, Brazil's Navy on Thursday began asking 30 oil tankers from 10 different countries for clarifications of their actions.

The environmental institute said 12 sea turtles and a bird have died after coming in contact with the crude oil.

Brazil's environmental protection agency has said it fears the oil spotted could just be a small fraction of what was spilled, noting there are some 2,000 kilometers (about 1,242 miles) of coastal line to monitor. The oil has been particularly hard to track as it floats under the surface of the water and can't be easily detected from planes.

This Oct. 4, 2019 handout photo released by the Aracaju Municipal Press Office, shows rocks stained by an oil spill, on Artistas Beach, in Aracaju, Brazil. The oil that has been polluting Brazil's northeastern beaches since early September is likely coming from Venezuela, according to a report by Brazil's state oil company cited by the country's environment minister. (Andre MoreiraAracaju Municipal Press Office via AP)

This Oct. 4, 2019 handout photo released by the Aracaju Municipal Press Office, shows rocks stained by an oil spill, on Artistas Beach, in Aracaju, Brazil. The oil that has been polluting Brazil's northeastern beaches since early September is likely coming from Venezuela, according to a report by Brazil's state oil company cited by the country's environment minister. (Andre MoreiraAracaju Municipal Press Office via AP)

In this Sept. 25, 2019 photo released by the Sergipe state Government, oil sludge floats near the rocks at the Coroa do Meio beach, in Sergipe state, Brazil. The spill started landing on Brazil's northeastern coast at the beginning of Sept., authorities say, and have now reached 61 municipalities in nine states, contaminating over 130 beaches. (Sergipe State Government via AP)

In this Sept. 25, 2019 photo released by the Sergipe state Government, oil sludge floats near the rocks at the Coroa do Meio beach, in Sergipe state, Brazil. The spill started landing on Brazil's northeastern coast at the beginning of Sept., authorities say, and have now reached 61 municipalities in nine states, contaminating over 130 beaches. (Sergipe State Government via AP)

In this Sept. 25, 2019 photo released by the Sergipe state Government, an oil spill covers a beach on Sergipe state, Brazil. The spill started landing on Brazil's northeastern coast at the beginning of Sept., authorities say, and have now reached 61 municipalities in nine states, contaminating over 130 beaches. (Sergipe State Government via AP)

In this Sept. 25, 2019 photo released by the Sergipe state Government, an oil spill covers a beach on Sergipe state, Brazil. The spill started landing on Brazil's northeastern coast at the beginning of Sept., authorities say, and have now reached 61 municipalities in nine states, contaminating over 130 beaches. (Sergipe State Government via AP)