Complex sentence: Originally a seasonally flooded river mouth marsh feed by Spencer Creek, it provided habitat to a wide variety of lifeforms, the habitat went into decline beginning in the late 19th century a result of water pollution, human overuse and the introduction of carp into Lake Ontario.
Split into simpler sentences: Originally a seasonally flooded river mouth marsh feed by Spencer Creek, it provided habitat to a wide variety of lifeforms. The habitat went into decline beginning in the late 19th century as a result of water pollution, human overuse, and the introduction of carp into Lake Ontario.