Columbia Crossings

In Washington, the Columbia River is crossable by car in 25 locations, including three ferries. 21 of those crossings are Washington state highways (US 101, SR 433, I-5, I-205, US 197, US 97, I-82, SR 397, US 395, I-182, SR 24, I-90, SR 285, US 2 [also signed US 97], US 97, SR 173, SR 17, SR 155, SR 21 [ferry], SR 20 [& US 395], SR 25).

Curiously (at least for me), the only US Routes and Interstates in Washington that don't cross the Columbia are I-405, I-705, US 195, US 730, and US 12 (technically, but it is signed crossing the river concurrent with I-182).

The other four river crossings are the Bridge of the Gods (near Stevenson), the Hood River Bridge (near White Salmon), the Wahkiakum County Ferry (near Cathlamet), and the Gifford-Inchelium Ferry (near Inchelium).

I've walked across the Bridge of the Gods as part of the Pacific Crest Trail. The bridge was built in the 1920s by a private toll company and named after a geological event. It's still a toll bridge (for vehicles -- no charge for pedestrians).

The Washington legislature told the DOT (via a new law in 1997) to build a new bridge near the Hood River Bridge (and call it SR 35), but that hasn't happened yet. The Hood River Bridge was constructed in the 1920s and its operated as a toll bridge by the Port of Hood River. They don't allow pedestrians.

The Wahkiakum County Ferry is operated by Wahkiakum County. It sails from the end of SR 409 across the river to US 30 in Oregon, every hour.

The Gifford-Inchelium Ferry is operated by the Colville Tribes. They don't charge anything for this trip across Roosevelt Lake.

The Columbia River has other crossings (railroads, dams, and a pedestrian bridge), but you're not allowed to drive over those. Here's a list.