There has been very little written in English or translated into English on the subject of the pre-xtian heathen Gods of the Low Countries (ie the Netherlands, Belgium and Luxembourg). The usual lame and lazy excuse is that there is no single homogenous mythology as the various tribes were not just Germanic but Gaulish or indeed perhaps Celto-Germanic. I believe that the myths, legends and folklore of this part of northern Europe could provide us with a rich and hitherto unmined source of Germanic mythology which may be particularly closely related to the continental Germanic and Anglo-Saxon mythologies.
I have in the past written about Nehalennia, Tanfana (a Northwest German/Netherlandic deity; see http://celto-germanic.blogspot.co.uk/2014/05/the-germanic-goddess-tamfana-and.html) and Fosite (see http://celto-germanic.blogspot.co.uk/2011/12/fositeforseti-aspect-of-thunor.html) but more often than not this has been part of wider issue than Netherlandic mythology. This is an oversight which I intend to correct in 2015. From toponymy, folklore and historical records we know that the Germanic peoples of continental Germania which includes the Germanic speaking parts of the Low Countries, revered literally hundreds of dieties. I will attempt to resurrect some of these deities during the course of the coming year. I have already made a small start in 2014. An example of this is the almost but not quite forgotten God Krodo from the closely situated Harz Mountains of Lower Saxony (see http://celto-germanic.blogspot.co.uk/2013/09/krodo-lost-saxon-god-traceable-to-aryan.html).
In addition to the lesser known deities the Germanic tribes of the Low Countries also worshipped the better known Gods, eg Wodan, Donar, Tyr and Frija. This is most evident from the Dutch days of the week: zondag, maandag, dinsdag, woensdag, donderdag, vrijdag and zaterdag.
A folktale from Gelderland in the eastern part of the Netherlands is very similar to the encounter of Thor against the Midgardsorm at Ragnarok:
This myth concerns a battle that allegedly took place between Donar the God of Thunder with the winter giants and the Midgaardsnake who strategically align against him. The giants throw hail down, while the snake climbs into a tall oak tree and blows poison into the air. Donar attacks, riding through the air on "his billy-goat wagon", the sky blazes and the earth trembles because of his "never missing thunderhammer." Donar strikes the snake on his head with such force on the head that not only was the monster crushed, the mighty thunderhammer went seven miles deep into the earth. The snake dies. However in the attack the snake's poison scorches and stuns Donar. Donar crashes down, with his "steerless goats" and wagon onto the Donderberg (meaning Donar's hill) in Dieren. Then the earth sank into the sea, the seagod blew a horn and a big black ship came to collect Donar's body. When the floodwaters receded, two lakes mark the spot that are "as deep as the world, the Uddelermeer or "Lake of Uddel" (Uttiloch), and the Godenmeer (God's lake)..." Later the legend continues that Thor's hammer surfaced from the depths. The grave of Migdaardsnake became overgrown with the forest nearby, until in 1222 a bright flame shot out of the pool and the ghost of the snake wriggled up and fled north. The forest was burned and a moor near the lake remains where the forest once was. (via Wikipedia)
The tale helps to eplain via the use of mythology how the Uddeler and Bleeke lakes were formed. Interestingly in addition to the reference to the Midgaardsnake being the cause of Donar's apparent death there is also an intriguing reference to His Hammer penetrating the ground for 7 miles, a motif clearly borrowed from the myth of the theft of Thor's Hammer by the Jotun Thrym! It would appear that the continental Germanic tribes did in fact share a common body of myth with the North Germanic Scandinavian peoples which has inevitably varied through the course of time and geography.