Fluids are seen in a wide range of disciplines, including mechanical, civil, chemical and biomedical engineering, geophysics, astrophysics and biology. In this paper, we investigate a -dimensional generalized Kadomtsev–Petviashvili equation for the long water waves and small-amplitude surface waves with the weak nonlinearity, weak dispersion and weak perturbation in a fluid. Breather-wave, lump-wave and lump wave–soliton solutions are derived under certain conditions via the Hirota method. With , where and represent the coefficients of dispersion and nonlinearity, respectively, we obtain the dark breather wave and lump wave. We observe the effects of , , , and on the dark breather wave and lump wave, where is the perturbed effect, and stand for the disturbed wave velocity effects corresponding to the and coordinates: and influence the amplitude of the dark breather wave; , and influence the distance between the adjacent valleys of the dark breather wave; , , and influence the location of the dark breather wave; , , and influence the amplitude of the dark lump wave; , and influence the width of the dark lump wave; , and influence the location of the dark lump wave. When , we present the fusion between a bright lump wave and one bright soliton as well as fission of one bright soliton. We also observe the fusion between a dark lump wave and one dark soliton as well as fission of one dark soliton with .