He watched the river flow.
( He ( ( watched ( the ( river flow ) ) ) . ) )
(ROOT (S (NP (PRP He)) (VP (VBD watched) (NP (DT the) (NN river) (NN flow))) (. .)))
The river levels were rising.
( ( The ( river levels ) ) ( ( were rising ) . ) )
(ROOT (S (NP (DT The) (NN river) (NNS levels)) (VP (VBD were) (VP (VBG rising))) (. .)))