The City without Night - S1.E62

As the 999 approaches the City Without Night, Maetel tells Tetsuro of a lake there, but tells him not to go out to see it. When they arrive on the planet, Tetsuro gets in trouble for going out at night, but is saved by Maetel. They are told that no one is allowed out at night because of a dangerous dinosaur, Heron, that lives in the lake. Tetsuro and Maetel head there anyway and help Heron when it is captured by some photographers. Heron actually is a friendly creature, and later helped Tetsuro and Maetel out when the police try to arrest them for the death of the photographers.