states as well as their stabilization. In cavity electro- and optomechanics, the control over mechanical oscillators relies on a dissipation hierarchy in which the electromagnetic energy decay rate significantly exceeds that of the mechanical oscillator. In contrast, recent theoretical work has considered the opposite regime in which the mechanical oscillator dissipation dominates and provides a cold dissipative reservoir to the electromagnetic degree of freedom. This novel regime allows to manipulate the electromagnetic mode and enables a new class of dissipative interactions. Here, we report on the experimental realization of this reversed dissipation regime in a microwave cavity optomechanical system. We directly evidence the preparation of a quasi-instantaneous, cold reservoir for a microwave field by on-demand decreasing or increasing the damping rate of the microwave mode, that corresponds to amplification and de-amplification of the microwave field. Moreover, we observe the onset of parametric instability, i.e. stimulated emission of microwaves (masing). The dissipative interaction additionally enables to operate the system as a low-noise, large-gain phase-preserving amplifier. Realizing a dissipative reservoir for microwave light is a requirement for the dissipative coupling of multiple cavity modes, which in turn forms the basis of dissipative quantum phase transitions, microwave entanglement schemes, and electromechanical quantum-limited amplifiers. Equally importantly, this interaction underpins recently predicted non-reciprocal devices, which would extend the available toolbox of quantum-limited microwave manipulation techniques.