In the 19th century, specific times of the year were named accordingly to seasonal changes and / or the activities individuals performed in their daily (bad season, theatrical season, carnival season and beautiful season). Regattas, which were maritime / nautical festivals seen in cities such as London and Marseille, were important urban actions of the beautiful season of Istanbul. These festivals functioned as urban social events that span a whole day. The first regatta in Istanbul was organized in 1859 with the attempts and under the patronage of British Ambassador Sir Henry Lytton Bulwer in different parts of the city such as Moda and Buyukdere, yet in time regattas became signature events of Buyukada. Regattas attracted the attention of all the citizens, especially the public officials, diplomats and bankers, namely the high society of Istanbul. Of the periodicals published in the 19th century, the turnout in the festivals in the 1870s was about 10,000 people. This very high level of participation brings into question the existence and extent of the effect of these events that could have transformed the places where these particular social events took place. From this perspective, such a transformative effect of an urban action can be investigated through the Buyukada regattas. There are no studies on the regattas of Buyukada and Istanbul in particular. However, the periodicals such as Journal de Constantinople, Levant Herald, Le Monde Illustre, Levant Herald and Eastern Express, Servet-i Funun, Malumat and memoirs written by the individuals like Samuel S. Cox and Lady Hornby who travelled Istanbul in the 19th century present primary evidence about the events. By applying these findings onto the Buyukada Map of Antoine Raymund, published in 1912, this paper analyses regattas' major effects on the formation, transformation and modernization of the urban space in the 19th century Istanbul.