The Houston Ship Channel closed for three days after a barge struck a highline electrical tower this past weekend, downing a power line stretching across the waterway to the busiest U.S. petrochemical port, the U.S. Coast Guard said.

More than 8 percent of U.S. refining capacity is upstream of where the power line blocks the channel.

The Coast Guard only shuts the channel for hurricanes and ship wrecks.

The channel is closed along a two-mile stretch near Baytown, Texas, a Coast Guard spokesman said.

One tanker was cleared through to the Exxon Mobil refinery in Baytown. The Coast Guard will allow some ships to pass "on a case-by-case basis, depending on where they're going," the spokesman said.

Texas City, Texas, where three refineries accounting for 5.5 percent of U.S. refining capacity are located, was not affected by the closure.

Bayport, Texans and the Barbour's Point Container Terminal were also not affected by the closure. (Reuters)