Two volcanic ranges, running roughly west to east, segment the country, but in between are broad, fertile valleys, such as that of the Lempa, the principal river. There are several fairly large lakes. El Salvador is the smallest Latin American republic and the most densely populated; overpopulation is a critical problem. The vast majority of the population is of mixed indigenous and European descent. Spanish is the official language. Roman Catholicism the dominant religion, but there is a growing minority who belong to evangelical Protestant churches.