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Attempts to create artificial tidal flats are being rolled out nationwide.
Literal
Artificial tidal-flat [object-を] construct attempts [subject-が] nationwide [adverbial-に] are-being-unfolded-[passive-ている].
Environmental/policy news register. 干潟 ('tidal flat') refers to the intertidal mudflats that support rich ecosystems. 人工干潟 ('artificial tidal flats') are human-made restorations, often created to offset lost habitat. 造成する 'to construct, to develop (land).' 試み 'attempt, endeavor' — the noun form of 試みる. 展開されている 'is being unfolded / deployed,' a passive continuous. 全国的に 'nationwide' — the suffix ~的 forms an adjectival-noun from many kango.