The intent of the proposed system was to develop an insitu biotreatment system for swine manure that should involve minimum handling by the farmer. A demonstration plant has been installed in the Paris region. The intensive lagooning system consists of algal ponds, daphnid ponds and a polishing fish pond working in series with a total area of 2100 m(2) and a total volume of 3600 m(3). The performance of the system was evaluated under winter conditions with raw decanted swine manure by measuring N-NH4+ and P-PO43- removal, pH, temperature, water oxygen, algal biomass and daphnid productions. Results showed that low temperatures (< 5 degrees C) did not allow any significant biomass production (0.41-0.68 g dry mass/m(2) d). Ammonia-nitrogen, mostly stripped (98% lost by stripping), and phosphate removals were small. However, as soon as the temperature increased in spring (March), ammonia-nitrogen removal was improved with a large contribution (71%) due to stripping and the algal productivity increased to approximate to 3.5 g dry mass/m(2) d; CO2 appeared to be a limiting factor. Ammonia-nitrogen, nitrate, nitrite and orthophosphate showed marked variations that could be correlated with manure overdoses.