A diode-pumped, actively Q-switched $2.8\mathrm{\mu m}$ fiber laser oscillator with an average output power of more than $12\mathrm{W}$ has been realized through the use of a $35\mathrm{\mu m}$ core erbium-doped ZBLAN fiber and an acousto-optic modulator; to our knowledge, this is the first $3\mathrm{\mu m}$ pulsed fiber laser in the $10\mathrm{W}$ class. Pulse energy up to $100\mathrm{\mu J}$ and pulse duration down to $90\mathrm{ns}$ , corresponding to a peak power of $0.9\mathrm{kW}$ , were achieved at a repetition rate of $120\mathrm{kHz}$ .