Suryaja is one among the numerous names of Yamuna River. The
river is known as Suryaja because she is the daughter of Surya, the sun god in
Hinduism.
Yamuna is the daughter of Surya and his wife Samjna. Samjna is daughter of
divine architect Vishwakarma.
As per Markandeya Purana, Surya approached Samjna, she being
unable to tolerate her brilliance closed her eyes in fear. Surya saw this as an
insult and cursed her to give birth to a River.
Thus, Yamuna is the daughter of Surya and in his wife Samjna
and is therefore also known as Suryaja.