river rising in the Loi Mountains of Laos and flowing southeastward through northern Vietnam to enter the Gulf of Tonkin near the city of Vinh after a course of 380 miles (612 km). The coastal riverine lowlands have relief features similar to those of the Red River; wide, level stretches of alluvium predominate with small undulation. There is a high population density in the river's delta region, particularly near Vinh. A low broken range of basaltic hills on the north side separates the Ca River delta from the deltas of the Ma and Chu rivers.