they are looking at some boats on the river是他们正在看河面上的一些船they are looking at some boats on the river的意思是他们正在看河面上的一些船,那么想问一下,如果说他们正在桥上看河面上的那些船应该怎么说呢,

the people who stand on the bridge are looking at some boats on the river.

they are looking at some boats on the river from the bridge.
或者说
Standing on the bridge,they are looking at some boats on the river.