The bar is currently holding all tiers. The rewards for each tier are following:
Tier 1 (25-30 frogs): Mudskipper hat;
Tier 2 (75-100 frogs): Water lily set cape;
Tier 3 (150-200 frogs): Water lily set hat;
Tier 4 (optional if you have the item previously, ~300-400 frogs): Blow kiss;
Tier 5 (500 frogs): Mudskipper morph.
Note: if you didn't get any of the previous years' rewards, you can obtain them this year by handing the frogs beyond the current year quest completion. Sadly, I can't tell how many frogs you need to give in order to get those.