Insufficiently excited plasmas generated in aqueous media with incompressibility and high thermal conductivity result in an anisotropic optical emission. The emission characteristics of underwater plasmas produced from an immersed Cu plate acquired with backward and lateral detections were investigated by irradiating with short and long pulse LIBS, respectively. We found that the plasma emission collected backward shows clear emission lines with high intensities by using long pulses, while different types of spectral lines were exhibited at different wavelengths using short pulses, including Fraunhofer-type absorption and broadened emission lines. For the lateral emission, it was unfortunately no remarkable spectral lines observed with a short pulse. By contrast, absorption lines at the resonant atomic lines of Cu and three emission lines near the wavelength of 515 nm were obtained simultaneously with a long pulse. Consequently, a weak intensity and wide line broadening occur in the spectral lines with the short pulse, while a long pulse can notably provide an enhanced line intensity and narrow line broadening. Since backward and lateral emissions exhibit significant differences, the use of long pulses allows for better observation of Fraunhofer-type absorption spectra in the lateral direction and better observation of emission spectra in the backward direction. There is a remarkable enhancement for the emission lines collected from the backward than those of the lateral direction with the line intensity being increased by more than 17 times. Therefore, a desired spectrum can be obtained by combining the lateral and backward collection methods with a long pulse. These results not only contribute to a better understanding of the radiation mechanisms in backward and lateral directions of underwater plasmas, but especially facilitate the qualitative and quantitative analysis of underwater LIBS.