The letter was signed by Democratic Sens. Patty Murray and Maria Cantwell, and Democratic Reps. Derek Kilmer, Denny Heck, Rick Larsen, Suzan DelBene, Jim McDermott and Adam Smith.
More than 82 million liters of untreated effluent is being dumped into our shared waters in the Strait of Juan de Fuca every day, the lawmakers said.
"This type of pollution is not only detrimental to ecosystem vitality, but also can have dire human health consequences. This is simply unacceptable," the delegation writes, urging Clark to work to find a solution so that "an appropriate treatment facility is completed as soon as possible."
"The strength of our economies in the Pacific Northwest and British Columbia depends on the health of our waterways and natural resources," the letter reads.
Gov. Jay Inslee sent a similar letter earlier in the week.
Last month, Clark's government refused to force the Victoria-area municipality of Esquimalt to accept the regional district's plans to locate a proposed $780 million treatment facility on the shores of the community.
The Victoria region's politicians have been scrambling ever since to develop a Plan B for sewage treatment.
Victoria is one of the few remaining Canadian cities that do little to treat its sewage, essentially pumping 34 million gallons of raw effluent daily into the strait, which connects to Puget Sound.
The letter from Inslee noted that in 1993, the state implemented a tourism boycott and cancelled major conferences and hotel bookings in Victoria. The two jurisdictions came to an agreement that same year that Victoria would have primary sewage treatment in place by 2002 and secondary treatment between 2008 and 2013, a deadline that was then pushed to 2018.
Talk of pushing the deadline once again, to 2020, "is not acceptable," Inslee wrote.
Earlier this week, B.C.'s environment minister, Mary Polak, said that the sewage treatment will happen.
"This is not up for debate," she said in a statement.