The 17-year-old from Hatfield took the title with 4,041 points across the series that incorporated legs in Italy, Sheffield and Berlin.
Canadian three-time Paralympic champion Aurelie Rivard (3,956) finished second and Netherlands’ Rio 2016 bronze medallist Chantalle Zijderveld (3,952) third.
She said: “It is shocking. There are so many athletes that are better than me. I did not expect all this to happen so quickly. I expected to come top 10 but not to win.”
Fiddes also won the junior title ahead of Zijderveld and Italy’s five-time world champion Carlotta Gilli (3,924).
The National Paralympic Committees’ title was awarded to Great Britain (15,742) who won the honour for a second year running. Netherlands (15,345) and Brazil (15,343) completed the podium.
British Para-Swimming’s National Performance Director, Chris Furber said: “We have seen some exceptional performances from our swimmer so far this year – facing difficult competition and many having to deliver performances around classification reviews.
“For Britain to top the world series rankings for a second year is not only a reflection of the hard work put in by our athletes but also by the world-class coaches and support staff we have in place.
“Louise has put in some great performances this year, taking two seconds off her PB in the 100m breaststroke in Sheffield, and earning three qualification standards for the European championships.
“With Dublin 2018 around the corner I am sure we will see more from Louise and all our other athletes.”
Daniel Dias from Brazil, and their most decorated Paralympian, successfully defended the men’s individual series title.
The scores for the overall rankings are calculated by adding up the swimmers’ two best point scores achieved in two different World Series events.
About British Swimming
British Swimming is the National Governing Body for Swimming, Para-Swimming, Diving, High Diving, Synchronised Swimming, Water Polo and Open Water in Great Britain. It is responsible internationally for the high performance representation of the sport. The members of British Swimming are the three Home Countries national governing bodies of England (Swim England), Scotland (Scottish Swimming) and Wales (Welsh ASA). British Swimming seeks to enable its athletes to achieve gold medal success at the Olympics, Paralympics, World Championships and Commonwealth Games.
About UK Sport
Every athlete who has received National Lottery funding will have a story to tell of the difference that it has made to their Olympic or Paralympic dream. But the simple truth is that the National Lottery has taken sport in the UK to a new level. Each successive Games proves that there is no longer any margin for error if you want the top prize. Medals are won and lost by the smallest possible margins – the power of UK Sport’s National Lottery investment is in its ability to seek out those tenths, hundredths or even thousandths of a second, wherever they exist, and make sure that if there’s a close call, British athletes emerge on the winning side.
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