Complex sentence: At some time the billabong overflowed and introduced Murray cod into the lake; they bred rapidly and from the 1850s to the 1890s Lake George abounded with Murray cod. The Federation Drought commenced in the mid- 1890s, and by 1902 the lake dried out completely.
Split into simpler sentences: At some time the billabong overflowed and introduced Murray cod into the lake itself. The long Federation Drought commenced in the mid- 1890s, and by 1902 the lake had dried out completely.