PROBLEM TO BE SOLVED: To provide a method for forming a fish reef block and seaweed bed, which reduces the possibility of flowing by a tidal current.SOLUTION: There is provided the fish reef block 10 in which a through-hole 12 is formed so as to penetrate from one surface through the other side surface. An opening area S1 of a first opening 12a at one side of the through-hole 12 is larger than the opening area S2 of a second opening 12b at the other side thereof and an aggregate as a raw material is water-granulated slag.【課題】潮流によって流される可能性が低減された漁礁ブロック及び藻場の形成方法を提供する。【解決手段】一の面から反対の側の面へ貫通する貫通孔１２が形成された漁礁ブロック１０において、貫通孔１２の一方の側の第１の開口部１２ａの開口面積Ｓ１が他方の側の第２の開口部１２ｂの開口面積Ｓ２よりも大きく、原材料としての骨材を水砕スラグとする。【選択図】図２
