We spent the afternoon and evening in the park and as far as I can tell we saw pretty much all of it. I advise that you spend no longer. The park is very enclosed so unlike Ngorongoro which we visited the following day, many of the animals are hidden from view.
Elephants, Impala, Giraffe, Hippopotami, Flamingos, Warthog, Zebras, Lizard of some kind.
Lion also live here but we saw none
Lake Manyara got its name from a plant the Masai used to built their boma with. The lake itself is 220sq km, while the park (since 1960 National Park) has an area of 330 sq km.
It is located at the foot of the Great Rift Escarpment, rising 600 meters high. Only 125 km from Arusha you can visit the park on a daytrip, but you can also stay the night in the park or just outside it on the escarpment.
The parks biosphere has lots to offer, about 350 birdspecies and many mammals like the zebra, wildebeest, giraffe, monkeys and elephants. But most famous are the treeclimbing lions.
It is very hard to find any hippo posing for photographer ;)))
Usully they are siting under water showing only nose to breath.