This study investigated the impacts of human activities on the marine fishing grounds along Mtwapa creek. The research study employed survey design, in which the researcher distributed both open-ended questionnaires and closed questionnaires to the respondent. The study population was divided into two clusters that is, marine officers and community fishermen. The sample size was 36 respondents, which is 30% of the target population. 21 respondents were selected from the community fishermen while the remaining 15 respondents were selected from marine officers. From the data collected it is evident that overfishing was the human activity that was rated the highest with 31% (20), closely followed by boat riding with 30% (19), dumping of waste in the ocean was rated third with 25% (16) and lastly, agricultural practices with 14% (9). On the Impacts of human activities marine fishing grounds, the study found that reduction of fish stock and loss of fish habitat were rated the highest with 26% (21), closely followed by loss of biodiversity and extinction 25% (20), and lastly pollution with 23% (19). The study concludes that different human activities were practiced in the study area with the main one being overfishing. Other activities practiced along Mtwapa Creek included dumping of waste, agricultural practices and boat riding. The effects of dumping of wastes into the ocean results into pollution this killing aquatic life. Agricultural activities also contributed to pollution of the ocean because of reliance on fertilizer application to improve yields and due to the methods of weeds and pests control used on the farms. All these practices negatively impact marine fishing grounds resulting in loss of biodiversity and extinction of some species.