。
Tom went splashing his way across the shallows.
Literal
Tom [subj-が] shallows [obj-を] splash-splash [adverb-と] walking went.
浅瀬 'shallows' is a compound from 浅 'shallow' + 瀬 'rapids / shoal,' typical of Japanese water-feature vocabulary. ぽちゃぽちゃ is a mimetic for the sound/feel of splashing in shallow water, used with the adverbial と. を here marks the path traversed (not a direct object) — a characteristic use of を with motion verbs. 歩いて行く is the 'going along on foot' compound with ~ていく marking motion away from the speaker.