夜(よる) yoruに ni泳(およ)ぐ() oyoguの noは wa危(き)険(けん) kikenです desu。 It's dangerous to swim at night. Literal Night [at-に] swim-[nom-のは] dangerous [copula-です]. Standard [verb]+のは+adjective pattern for 'it is [adjective] to [verb].' 泳ぐ ('swim') is the base verb. 危険 is the na-adjective 'dangerous.' nightsafety and danger~のは (nominalized topic)
夜(よる) yoruに ni泳(およ)ぐ() oyoguの noは wa危(き)険(けん) kikenです desu。 It's dangerous to swim at night. Literal Night [at-に] swim-[nom-のは] dangerous [copula-です]. Standard [verb]+のは+adjective pattern for 'it is [adjective] to [verb].' 泳ぐ ('swim') is the base verb. 危険 is the na-adjective 'dangerous.' nightsafety and danger~のは (nominalized topic)