Members of the San Diego Regional Water Quality Control Board have agreed to take the first step toward filing a lawsuit against the federal government to stem the cross-border flow of contaminated water into the Tijuana River Valley. Voting in a closed session on Monday, board members authorized staff to prepare a 60-day notice of intent to litigate against the U.S. International Boundary and Water Commission for violations of the Clean Water Act. David Gibson, the board’s executive officer, said the state agency will offer details of the decision in a statement that will be released in coming days.