This image shows one of the common pleasure boats that cruise along the river. There is also a business in river cruises, which commonly include larger boats with low overheads so they can pass under the many bridges.
The description states:
SAN ANTONIO RIVER
San Antonio, Texas
Winding through the downtown area the river is lined with beautiful parkways and walks. It also affords pleasant boating.
–The river itself is normally quite green and muddy looking even though cleaned once a year.
This image dates from the 1960s.