Bristol Zoo had to shut its gates after about 3,000 people turned up for a Pokémon Go event.
The zoo said it expected the event, held on Wednesday evening, to attract about 500 people, but ended up having to turn about 1,000 gamers away after letting 2,000 in.
The popular game involves people catching virtual creatures in real-world locations, which they then use to battle each other.
The zoo said it had used special in-game items that would cause more of the imaginary monsters to appear on its premises for the duration of the event.
It said a large queue of Pokémon collectors had formed for the event an hour before it began.
The zoo, which operates as a charity under the name the Bristol Zoological Society, said it raised about £4,500 from the event – it was free, but the zoo asked for a suggested donation of £3 per person.
It warned players not to enter animal enclosures and said "not even a charizard could take on our lions and come out unscathed".
The zoo plans to run another event next Wednesday, although this time it is asking people to reserve tickets in advance, with 2,500 available.