(CNN) -- Efforts to clean up a 168,000 gallons of thick, viscous oil that spilled into the Port of Houston near Galveston, Texas, stretched into a third day Tuesday, as wildlife rescuers sought to estimate the impact on birds and marine life.
The spill, which occurred over the weekend after two vessels collided, has forced the closure of the heavily trafficked port, putting dozens of ships in limbo as they wait in a queue to enter and exit the waterway early Tuesday afternoon.
The Houston Ship Channel was opened to limited barge traffic within the channel, U.S. Coast Guard Petty Officer Andy Kendrick said, but the channel remained closed to all other vessels, and the vessels in the port were not allowed to leave.
As of early Tuesday afternoon, 101 inbound and outbound vessels were stuck in the channel, Kendrick said.
On Galveston Island, the cruise terminal is loaded with passengers waiting for ships docked at sea, while cruise ships waiting to get to port are stuck on the water.
The U.S. Coast Guard and other agencies are evaluating whether portions of the busy shipping channel can be reopened, pending the "skimming and booming" efforts under way to contain the environmental disaster.
Meanwhile, the Galveston Bolivar ferry has been granted permission to run amid efforts to clean the port and locate affected wildlife.
According to authorities leading the joint effort to contain the spill, there have been 18 birds captured, 10 deceased, and eight "oiled" but not captured. There have also been sightings of oiled birds that have yet to be confirmed.
Texas Parks and Wildlife Department personnel said they are continuing to look for affected wildlife in Bolivar Flats, which is considered a significant refuge for birds.
"Galveston Bay is one of America's greatest estuaries and an important home to Texas seafood providers and recreational fishermen as well as the entry point to the Port of Houston. While the area has long dealt with many pollution concerns, this spill is significant," said scientist Doug Rader of the nonprofit Environmental Defense Fund.
"In the early stages of this spill much remains unknown, but for shrimp, blue crab, menhaden and other marine life, which rely on the bay as an essential nursery, further investigation and long-term monitoring within the footprint of this spill is necessary."
Approximately 15.5 miles of nonconsecutive shoreline have been impacted, and more than 750 people are working to resolve the spill, officials said.
The Coast Guard said they will continue their investigation.