It is located in Pastoria City in Sinnoh which can also have pokemon that can not be found anywhere else in Sinnoh. It costs P500 to enter and you will recieve 30 Safari balls to catch Pokemons. This place has 6 different areas in it and each one of them has certain pokemon in them.
Pokemon
054 Psyduck
299 Azurill
183 Marill
194 Wooper
195 Quagsire
399 Bidoof
400 Bibarel
397 Starly (Morning and day only)
408 Budew (Morning and Day only)
163 Hoothoot (Night only)
164 Noctowl (Night only)
024 Arbok (Only by inserting the FireRed cartidge after recieving the National Pokedex)
129 Magikarp (Old and Good Rod)
130 Gyarados (Good and Super Rod)
318 Carvanha (Super Rod)
339 Barboach (Good Rod)
340 Whiscash (Super Rod)
055 Golduck
193 Yanma (National Pokedex)
398 Staravia
451 Skorupi
453 Croagunk
046 Paras (National Pokedex)
102 Exeggcute (National Pokedex)
115 Kangaskhan (National Pokedex)
265 Shroomish (National Pokedex)
Pastoria Great Marsh