Corrosion rate of stainless, mild and carbon steel coupons in New Calabar River and Ndoni River was monitored monthly for a period of one year. Corrosion rate was determined by weight loss. Carbon steel had corrosion rate of 72g/yr, mild steel 39g/yr, stainless steel 1.3g/yr in New Calabar River while carbon steel had corrosion rate of 44g/yr, mild steel 27g/yr, stainless steel 0.64g/yr in Ndoni River. Micro-organisms isolated include Sulphur reducing bacteria, Iron bacteria and Sulphur bacteria. In New Calabar River weight loss of stainless, mild and carbon steel showed these trend for rainy season (April-October) respectively; (0-0.112)g, (1.864-2.139)g (2.113-4.230)g. The dry season (November-March) showed these trend respectively; (0.117-0.141)g, (2.147-8.001)g, (4.272-15.171)g. In fresh water weight loss of stainless, mild and carbon steel for rainy season (April-October) respectively showed the following trend (0-0.030)g, (0.695-1.568)g, (1.000-2.316)g, while the dry season (November-March) respectively showed these trend (0.044-0.111)g, (1.586-5.771)g, (2.325-9.131)g. In New Calabar River corrosion rate of stainless, mild and carbon steel showed these trend for rainy season (April-October) respectively; (0-0.016)g/month, (1.864-0.306)g/month, (2.113-0.604)g/month. The trend for dry season (November-March) respectively was (0.014-0.012)g/month, (0.268-0.667)g/month, (0.534-1.264)g/month. In Ndoni River, the corrosion rate of stainless, mild and carbon steel for rainy season (April-October) respectively showed these trend (0-0.004)g/month, (0.695-0.244)g/month, (1.000-0.331)g/month while the dry season (November-March) respectively showed these trend (0.006-0.009)g/month, (0.198-0.481)g/month, (0.291-0.761)g/month. Total Dissolved Solids, Total Suspended Solids, Total Organic Carbon, Biochemical Oxygen Demand, Conductivity, Salinity, Oil and Grease, Chloride, Sulphate Sulphite, Temperature, pH were monitored for rainy season and dry season in both New Calabar River and Ndoni River. The study was able to show that corrosion rate was higher in New Calabar River than Ndoni River in same steel types comparatively especially in the dry seasons. Stainless steel if not yet in use should be encouraged in pipeline work in oil industries and other related works since it is less bio- corrosive in both New Calabar River and Ndoni River. Lots of emphasis should be laid on microbial influenced corrosion since it has proved to be a menace in corrosion.
