Questions & Answers about gwairi mure tteoyo.
뜨다 is an “ㅡ”-irregular verb. When adding a vowel suffix like -어요, you drop the stem vowel ㅡ and replace it with ㅓ.
• 뜨다 → 뜨 + 어요 → drop ㅡ → 떠요
• 떠요 is simple present; it describes a present state or habitual action (“floats”).
• 떠 있어요 uses the progressive/stative construction -아/어 있다, emphasizing “is in the state of floating right now.” In many contexts they’re interchangeable, but 떠 있어요 more strongly highlights “ongoing state.”