。
Japanese irises were blooming beautifully by the edge of the pond.
Literal
Pond [genitive-の] edge [at-に] flower-iris [subject-が] beautifully were-blooming.
A short descriptive sentence in plain written style. ほとり (辺) is a slightly literary word for 'edge / bank / shore,' used especially of bodies of water — you'd say 池のほとり but not 道のほとり (for the latter you'd use 道端). 花ショウブ (花菖蒲, はなしょうぶ) is the Japanese iris, a culturally significant flower associated with early summer and Boy's Day (端午の節句). The ~ていました form marks not an ongoing action but the resulting state ('were in bloom'), since 咲く is a change-of-state verb.