Abstract Purpose Excessive light causes both damage to the photoreceptors and pigment epithelium, and degenerative alterations in the inner retina, for example apoptotic death of ganglion cells and a decrease in the thickness of the inner plexiform layer. We investigated whether gliotic alterations of Müller cells may contribute to the light‐evoked degenerative alterations in the inner retina. Methods Retinas of adult rats were exposed to blue light for 30 minutes. At various time periods after treatment, retinal slices were immunostained against potassium and water channel proteins. Recordings of potassium currents were made in isolated Müller cells, and the swelling of Müller cell bodies was recorded in retinal slices. Results After blue light treatment, Müller cells displayed hypertrophy and an increase in glial fibrillary acidic protein. The immunostaining of the glial water channel aquaporin‐4 was increased in the outer retina while the immunostaining of the photoreceptor water channel aquaporin‐1 disappeared. Blue light treatment resulted in a decrease and mislocation of the glial Kir4.1 protein in the whole retinal tissue, and a decrease in the potassium conductance of Müller cells. Hypoosmotic stress evoked a swelling of Müller cell bodies in blue light‐treated retinas that was not observed in control tissues. Conclusion Gliosis of Müller cells associated with a loss of functional Kir4.1 channels will result in a disturbance of the retinal potassium and water homeostasis contributing to the degenerative alterations of the inner retina after exposure to blue light.