The U.S. Coast Guard on Tuesday allowed limited access to shipping traffic in a 3-mile stretch of the Mississippi River near Convent after the Monday afternoon collisions of three vessels led to the release of crude oil into the water.

The restrictions came as the Coast Guard sent out a shoreline team and flew over sections of the Mississippi to see if oil had collected along the shore or if sheen was visible on the water, the Coast Guard said in a news release.

No oil could be seen along the shore or elsewhere on the water with the exception of a small amount of sheen where one of the two collisions happened, Coast Guard officials said.

A Coast Guard helicopter flew over an 85-mile stretch of the river from a spot just past English Turn below New Orleans to the Shell Oil dock just downstream of the Sunshine Bridge in the search for oil sheen, the Coast Guard said.

A Coast Guard vessel also checked for oil along the shore between Gretna and the same oil dock near the Sunshine Bridge and spotted no recoverable oil.

Oil clean up operations for the 420 gallons that did spill into the river were continuing late Tuesday, the Coast Guard said.

Meanwhile, one vessel at a time was allowed through the restricted zone between mile markers 160 and 163 in the Convent area, Petty Officer 2nd Class Seth Johnson said.

Previously, the collisions had completely shut traffic over a 9-mile stretch of the river until 10 p.m. Monday. The former closure area encompassed the current 3-mile limited-access zone.

The collisions began about 4 p.m. Monday when the Privocean, a bulk carrier, broke free from its mooring at the Illinois Central Marine Terminal on the east bank of the river near Convent and drifted downstream.

The Privocean first struck the Texas, a tow boat that was moored but had some of its crew aboard, and then drifted farther downriver to hit the Bravo on the west bank of the river at the Ergon terminal in the St. James area.

The Coast Guard did not say as of Tuesday evening what caused the Privocean to break free initially, but an investigation is underway.

The west bank section of the river where the collisions happened includes several oil terminals tied to tank farms and other facilities, including Ergon, Capline and Nustar.

Moments before the crash, the Bravo’s crew had been offloading crude oil from the 816-foot tank ship into the Ergon terminal, the Coast Guard said.

The Bravo was able to finish an emergency shutdown before breaking free of its moorings and connection points, the Coast Guard said, avoiding a bigger oil spill. The oil spill came from the crude left in the terminal’s connection arms after the Bravo broke free, the Coast Guard said.

After the oil leaked into the river, the Coast Guard warned communities down river to protect water supplies, but St. James Parish officials said late Monday their water intake points on the river were open and safe.

About 126 gallons of oil were also spilled on deck of the Bravo, but the oil was contained and cleaned.

After hitting both vessels Monday and traveling a half-mile down river, the Privocean’s crew was able to get ship underway — it had been moored for cargo operations when it broke free — and anchor it at river mile marker 162.

The Bravo and Privocean, which are both Maltese-flagged ships, were being monitored by the Coast Guard.

The Bravo, a single-hulled tanker, was taking on water in its ballast tanks right after the collision but the Coast Guard said the water was being pumped out. The vessel was moored at the Ergon terminal late Tuesday morning.

Coast Guard officials said a mooring line also had fouled the Bravo’s propeller, but they said diving operations to finish damage assessments of the Bravo and other vessels remain pending due to poor visibility in the river.

Crews with OMI Environmental Solutions could be seen putting out protective oil boom mid-morning Tuesday along the piers of the Ergon terminal.

Connie Baer, spokeswoman for OMI, said the boom was being put out as a precautionary measure under the direction of the Coast Guard, which is in charge of the collision response, and was not an indication of additional oil leaking from the Bravo.

The crew of the Texas was taken to a hospital Monday, but no injuries were reported.

Johnson said the 98-foot towboat began taking on water Monday after the collision with the 44,619-ton Privocean but the crew of the Texas ran the ship ashore to prevent it from sinking.

According to the Coast Guard, the towboat is now stable and remains pushed up on the river bank near milepost 162.

According to the DNV GL website, a risk management company, the Privocean was built in 2013 and is owned by Privocean Shipping and managed by Bariba Corp. Both are Greek shipping companies.

The Bravo, built in 2011, is being managed by a Turkish shipping company, Genel Denizcilik Nakliyati A.S., the DNV GL website says. The Texas is owned by Crescent Towing of New Orleans, the Coast Guard said.

The Privocean, which had minor damage, remains moored in the Mississippi in St. James Parish at milepost 162, the Coast Guard said.

Follow David J. Mitchell on Twitter, @NewsieDave.