Final answer:
The river next to Boathouse Row in Philadelphia is the Schuylkill River, a historical part of the city known for rowing.
Step-by-step explanation:
The river next to Boathouse Row in Philadelphia is the Schuylkill River. Boathouse Row is a historic site located along the eastern bank of the Schuylkill River.
It consists of a row of 19th-century boathouses which are home to social and rowing clubs and are iconic landmarks in the city. This river is known for its rowing regattas and is a major part of Philadelphia's history.