Translation:The animals see themselves in the water.
The “si passivante”, as I said, is used in passive constructions and it is formed as: si + 3rd singular/plural person of a transitive verb (according to the “object” of the starting sentence). Like this, you avoid to write the usual passive form of the verb, ‘essere’ or ‘venire’ + past participle, but only for those two personas: it doesn’t work for the 1st and 2nd singular/plural person.
Qui si vendono i biglietti del bus = Qui sono venduti i biglietti del bus => Here are sold the bus tickets. In estate si mangia il gelato. = In summer you eat ice cream = ice cream is eaten // In estate si mangiano i gelati. => In summer you eat ice creams = ice creams are eaten