Abstract: This work presents the multispectral reconstruction of the vertical profile of chlorophyll concentration (CHL) in Case-1 waters. We consider that absorption, transmission and scattering of light in such waters are most influenced by the presence of phytoplankton being its optical properties given by CHL. The vertical profile of CHL is reconstructed from experimental measurements of water-leaving radiances (nLw) at 10 wavelengths. These radiances are considered for a discrete number of upward polar directions. This inverse problem is solved by an Ant Colony Optimization (ACO) algorithm using a recent regularization scheme based on the pre-selection of the smoother candidate solutions. The multispectral approach allows estimating the vertical profile using only nLw, instead of measurements in several depths. The inverse problem is formulated as an optimization problem and iteratively solved by the ACO using the radiative transfer equation as direct model. An objective function is given by the square difference between computed and experimental radiances. At each iteration a population of candidate solutions is generated, pre-selected and evaluated by means of the objective function. Each candidate solution corresponds to a discrete CHL profile. The radiative transfer equation is solved for each candidate solution yielding the radiances that are used in the objective function to evaluate it. Since this equation requires the absorption and scattering coefficients, these are calculated using bio-optical models, relating optical coefficients with CHL. The radiative transfer equation is solved using the Laplace transform discrete ordinate LTS_N method. A parallel implementation of the ACO is employed and executed in a distributed memory machine.