Tens of thousands of demonstrators, including musicians and children, took to the streets of Barcelona yesterday to protest a massive $23 billion water diversion project in Spain. The plan, which is now before the country’s parliament for final approval, would divert the Ebro River in the northeast and involve the construction of 120 dams to bring water to the dry southeastern parts of the country. Activists say the project would benefit developers and the electricity industry at the expense of the environment. They estimate that yesterday’s protest drew 300,000, while police say 80,000 attended. More than 400,000 protested the plan last October in the city of Zaragoza; a third protest is scheduled for next month in Madrid.