The impact of an oil spill that temporarily shut down the Houston Ship Channel, one of the United States' busiest waterways, still lingers and could have lasting effects on the undersea ecosystem in the Gulf of Mexico, experts said Sunday. Quarter-sized tar balls were spotted hundreds of miles away from the channel at a popular tourist island in southwest Texas as the oil continues to drift down the Gulf, the Houston Chronicle reported. The tar balls washed up Sunday in Mustang Island State Park, a barrier island near Corpus Christi, about 200 miles (320 km) from the site of the March 22 spill, according to the report. Tyrone Conner of the U.S. Coast Guard told the media a crew of about 90 workers had been deployed to clean up the tar balls that are soiling a 22-mile stretch of coast. Though the Houston channel has resumed round-the-clock operations on Thursday, clean-up work has not been finished as high wind and choppy waves spread the oil farther into the Gulf. Some experts earlier downplayed the oil spill, saying that it falls far short of the infamous 2010 BP oil spill which killed 11 workers and dumped millions of barrels of oil into the Gulf of Mexico. Others still worry the 170,000 gallons of oil spilled could have lasting effects on the environment. Antionetta Quigg, a marine biology professor at Texas A&M University at Galveston, told the Galveston County Daily News that based on previous studies, the oil has been found to be toxic and can make plankton toxic too, which means fish in the polluted water get a "double hit" from oil both in their physical environment and food sources. Some of the oil picking up sediment could have sunk to the seabed and could smother or poison animals like shrimp or crabs, Quigg said. Their demise, in turn, affects the food chain of the bay. State officials late last week issued a seafood consumption advisory for Galveston Bay and the Gulf of Mexico that recommends fish, shrimp or crab from water where oil is present not be eaten. The oil spill happened on March 22 when a bulk vessel collided with a barge carrying nearly a million gallons of fuel in the Houston Ship Channel. The collision damaged a compartment on the barge and released 4,000 barrels of oil, or 168,000 gallons of oil. Hundreds of vessels ground to a halt due to the spill. It' s still unknown what caused the collision.