Great Marsh

The Great Marsh is the Sinnoh Safari Zone. Separated into six areas accessible by a small train, this Safari Zone has you go around a swamp to look for various Pokémon. These areas are interconnected with various bridges

When you go in, it will cost 500 to enter and you will be given 30 Safari Balls and can only make a 500 steps before you get called back, though you can quit at any time.

As the wild encounters take place in the swamp area, if you hit an area with deep swamp, you can get pulled in and will have to move a lot to get out.

Catching Pokémon works similar to past Safari Zones in that you can't battle the Pokémon but rather have to utilise a new mechanic to catch them. This involves you using Bait or Mud to alter the capabilities of the Pokémon. Unlike the standard wild encounters outside of the Great Martsh, each Pokémon has got a chance of fleeing.

If you use Mud, the Pokémon will be less likely to flee, but may be harder to catch
If you throw Bait, the Pokémon will be more likely to flee, but easier to catch.

Each day, a special Pokémon will spawn in each area of the Great Marsh. If you go upstairs in the main gate of the Great Marsh, you will be able to look through binoculars for 100. This will give you a look at 6 areas of the Great Marsh and will focus on a specific Pokémon in each area. It will show you the special Pokémon during this. Looking multiple times won't change the spawn and the spawn will happen even if you don't look through the binoculars

Many Pokémon such as Carnivine are exclusive to this method, and the Pokémon you can find through it increase when you obtain the National Pokédex.